This paper presents a novel lens-free on-chip 3D microscopy technique called wavelength-scanning Fourier ptychographic diffraction tomography (wsFPDT), which enables high-throughput, label-free 3D tomographic imaging with quasi-uniform, pixel-super-resolved resolution across the full field-of-view (FOV) of the image sensor. Unlike traditional lens-free microscopy methods that use angularly-variable illuminations, wsFPDT employs on-axis wavelength-variable illumination ranging from 430 to 1200 nm. The corresponding under-sampled diffraction patterns are processed using an iterative ptychographic reconstruction algorithm to recover the 3D refractive index (RI) distribution of the sample. This method eliminates the need for mechanical motion during image acquisition and precise registration of the raw images, achieving a quasi-uniform imaging resolution across the entire FOV. The wsFPDT method demonstrates high-throughput, billion-voxel 3D tomographic imaging results with a half-pitch lateral resolution of 775 nm and an axial resolution of 5.43 μm across a large FOV of 29.85 mm² and an imaging depth of over 200 μm. The effectiveness of the method was validated by imaging various samples, including micro-polystyrene beads, diatoms, and mouse mononuclear macrophage cells. The unique capability of wsFPDT to reveal quantitative morphological properties, such as area, volume, and sphericity index of single cells over large cell populations, makes it a powerful quantitative and label-free tool for high-throughput biological applications. The method also offers a decent spatial resolution and quantitative 3D RI imaging capability across a large imaging volume, benefiting various high-throughput biological and biomedical applications. The wsFPDT method is compared with conventional lens-based FPDT and SS-OCT methods, showing its advantages in terms of simplicity, speed, and resolution. The method is also compared with other lens-free on-chip tomography techniques, demonstrating its effectiveness in reconstructing 3D RI distributions of thick biological samples. The method is further validated through experiments on phase resolution targets, diatom samples, and mouse mononuclear macrophage cells, showing its ability to achieve quasi-uniform and pixel-super-resolved RI recovery across the full FOV. The method is also compared with traditional ODT techniques, showing its advantages in terms of resolution, speed, and simplicity. The method is also compared with other computational imaging techniques, showing its effectiveness in achieving high-resolution 3D tomographic imaging. The method is also compared with other lens-free on-chip tomography techniques, demonstrating its effectiveness in reconstructing 3D RI distributions of thick biological samples. The method is further validated through experiments on phase resolution targets, diatom samples, and mouse mononuclear macrophage cells, showing its ability to achieve quasi-uniform and pixel-superThis paper presents a novel lens-free on-chip 3D microscopy technique called wavelength-scanning Fourier ptychographic diffraction tomography (wsFPDT), which enables high-throughput, label-free 3D tomographic imaging with quasi-uniform, pixel-super-resolved resolution across the full field-of-view (FOV) of the image sensor. Unlike traditional lens-free microscopy methods that use angularly-variable illuminations, wsFPDT employs on-axis wavelength-variable illumination ranging from 430 to 1200 nm. The corresponding under-sampled diffraction patterns are processed using an iterative ptychographic reconstruction algorithm to recover the 3D refractive index (RI) distribution of the sample. This method eliminates the need for mechanical motion during image acquisition and precise registration of the raw images, achieving a quasi-uniform imaging resolution across the entire FOV. The wsFPDT method demonstrates high-throughput, billion-voxel 3D tomographic imaging results with a half-pitch lateral resolution of 775 nm and an axial resolution of 5.43 μm across a large FOV of 29.85 mm² and an imaging depth of over 200 μm. The effectiveness of the method was validated by imaging various samples, including micro-polystyrene beads, diatoms, and mouse mononuclear macrophage cells. The unique capability of wsFPDT to reveal quantitative morphological properties, such as area, volume, and sphericity index of single cells over large cell populations, makes it a powerful quantitative and label-free tool for high-throughput biological applications. The method also offers a decent spatial resolution and quantitative 3D RI imaging capability across a large imaging volume, benefiting various high-throughput biological and biomedical applications. The wsFPDT method is compared with conventional lens-based FPDT and SS-OCT methods, showing its advantages in terms of simplicity, speed, and resolution. The method is also compared with other lens-free on-chip tomography techniques, demonstrating its effectiveness in reconstructing 3D RI distributions of thick biological samples. The method is further validated through experiments on phase resolution targets, diatom samples, and mouse mononuclear macrophage cells, showing its ability to achieve quasi-uniform and pixel-super-resolved RI recovery across the full FOV. The method is also compared with traditional ODT techniques, showing its advantages in terms of resolution, speed, and simplicity. The method is also compared with other computational imaging techniques, showing its effectiveness in achieving high-resolution 3D tomographic imaging. The method is also compared with other lens-free on-chip tomography techniques, demonstrating its effectiveness in reconstructing 3D RI distributions of thick biological samples. The method is further validated through experiments on phase resolution targets, diatom samples, and mouse mononuclear macrophage cells, showing its ability to achieve quasi-uniform and pixel-super