This study investigates the Soret effect in the magnetohydrodynamics (MHD) flow of a Casson fluid over an oscillating vertical plate using a constant proportional Caputo (CPC) fractional derivative. The CPC fractional derivative combines the proportional and Caputo operators, providing a novel tool for analyzing non-Newtonian fluid flow. The governing partial differential equations (PDEs) are transformed into dimensionless form using appropriate nondimensional variables, and the Laplace transform method is applied to solve them. The results are presented graphically for velocity, concentration, and temperature profiles, and the effects of various parameters such as the Prandtl number, fractional parameters, and Soret number are analyzed. The study finds that the velocity, temperature, and concentration profiles are influenced by the Grashof number, Schmidt number, and Soret number. The velocity increases with the Grashof and mass Grashof numbers but decreases with the Prandtl and Schmidt numbers. The temperature and concentration profiles are affected by the fractional parameters, with higher values leading to more pronounced decay. The Soret effect enhances the mass flux and can be relevant in biomedical applications, such as drug delivery systems, and in the oil and gas industry, particularly in enhanced oil recovery techniques. The study also highlights the potential of the CPC fractional derivative in improving the efficiency of heat exchangers and chemical reactors.This study investigates the Soret effect in the magnetohydrodynamics (MHD) flow of a Casson fluid over an oscillating vertical plate using a constant proportional Caputo (CPC) fractional derivative. The CPC fractional derivative combines the proportional and Caputo operators, providing a novel tool for analyzing non-Newtonian fluid flow. The governing partial differential equations (PDEs) are transformed into dimensionless form using appropriate nondimensional variables, and the Laplace transform method is applied to solve them. The results are presented graphically for velocity, concentration, and temperature profiles, and the effects of various parameters such as the Prandtl number, fractional parameters, and Soret number are analyzed. The study finds that the velocity, temperature, and concentration profiles are influenced by the Grashof number, Schmidt number, and Soret number. The velocity increases with the Grashof and mass Grashof numbers but decreases with the Prandtl and Schmidt numbers. The temperature and concentration profiles are affected by the fractional parameters, with higher values leading to more pronounced decay. The Soret effect enhances the mass flux and can be relevant in biomedical applications, such as drug delivery systems, and in the oil and gas industry, particularly in enhanced oil recovery techniques. The study also highlights the potential of the CPC fractional derivative in improving the efficiency of heat exchangers and chemical reactors.