A negative refractive index (n') of approximately -0.3 was experimentally observed in an array of pairs of parallel gold nanorods at an optical communication wavelength of 1.5 μm. This effect arises from plasmon resonance in the nanorod pairs for both electric and magnetic components of light. The refractive index was determined from phase and amplitude measurements of transmission and reflection, which matched finite difference time domain (FDTD) simulations. The phase of the transmitted wave is critical for determining n', emphasizing the importance of phase measurements. Negative-index materials (NIMs) have a negative refractive index, causing electromagnetic waves to propagate in the opposite direction of energy flow. While naturally occurring NIMs are rare, metamaterials can be engineered to exhibit this property. Recent experiments have demonstrated that NIMs can be achieved in the terahertz range, but the ultimate goal of negative refraction has not yet been fully realized. This study reports the first experimental observation of negative refraction in the optical range, specifically near 1.5 μm. The design of the NIM structure was based on a theoretical prediction of negative refraction in a layer of pairs of parallel metal nanorods. The optical characteristics of the nanorod array were simulated using 3D FDTD, showing good agreement with experimental data. The refractive index was calculated using a formula derived from the measured phase and amplitude data. The experimental results showed strong plasmonic resonance near 1.3 μm for light polarized parallel to the nanorods, with both electric and magnetic responses. For light polarized perpendicular to the rods, only the electric response was significant. The phase measurements using polarization and walk-off interferometers confirmed that the phase and group velocities of light are antiparallel in NIMs, unlike in normal materials. The refractive index was found to be negative between 1.1 and 1.4 μm, reaching a magnitude of approximately -0.15 at 1.25 μm. The negative refractive index was confirmed in both samples with and without an ITO layer, showing good agreement between experimental and simulated data. The results demonstrate that the array of pairs of parallel gold nanorods can be used to achieve negative refraction in the optical range, opening new possibilities for optical applications. The refractive index depends on the size and separation of the nanorods, and can be optimized to reduce losses and increase the magnitude of negative refraction.A negative refractive index (n') of approximately -0.3 was experimentally observed in an array of pairs of parallel gold nanorods at an optical communication wavelength of 1.5 μm. This effect arises from plasmon resonance in the nanorod pairs for both electric and magnetic components of light. The refractive index was determined from phase and amplitude measurements of transmission and reflection, which matched finite difference time domain (FDTD) simulations. The phase of the transmitted wave is critical for determining n', emphasizing the importance of phase measurements. Negative-index materials (NIMs) have a negative refractive index, causing electromagnetic waves to propagate in the opposite direction of energy flow. While naturally occurring NIMs are rare, metamaterials can be engineered to exhibit this property. Recent experiments have demonstrated that NIMs can be achieved in the terahertz range, but the ultimate goal of negative refraction has not yet been fully realized. This study reports the first experimental observation of negative refraction in the optical range, specifically near 1.5 μm. The design of the NIM structure was based on a theoretical prediction of negative refraction in a layer of pairs of parallel metal nanorods. The optical characteristics of the nanorod array were simulated using 3D FDTD, showing good agreement with experimental data. The refractive index was calculated using a formula derived from the measured phase and amplitude data. The experimental results showed strong plasmonic resonance near 1.3 μm for light polarized parallel to the nanorods, with both electric and magnetic responses. For light polarized perpendicular to the rods, only the electric response was significant. The phase measurements using polarization and walk-off interferometers confirmed that the phase and group velocities of light are antiparallel in NIMs, unlike in normal materials. The refractive index was found to be negative between 1.1 and 1.4 μm, reaching a magnitude of approximately -0.15 at 1.25 μm. The negative refractive index was confirmed in both samples with and without an ITO layer, showing good agreement between experimental and simulated data. The results demonstrate that the array of pairs of parallel gold nanorods can be used to achieve negative refraction in the optical range, opening new possibilities for optical applications. The refractive index depends on the size and separation of the nanorods, and can be optimized to reduce losses and increase the magnitude of negative refraction.