In this paper, the performance of a fiber optic sensor based on surface Plasmon resonance, coated with nanoparticles of gold and tellurium oxide was theoretically investigated. In this structure, part of the single-mode fiber clad was removed and replaced with a layer of gold and tellurium oxide nanoparticles. The spectrum of transmitted power and sensitivity of the sensor is plotted for a layer with a thickness of 50 nm for different values of volume filling factor. According to the results, the changes in the volume filling factor are directly related to the resonant wavelength and the sensitivity of the sensor, and the resonant wavelength increases with increasing the thickness of the nanostructure layer. According to the obtained results, this tool shows high sensitivity in aqueous media at visible wavelength (600 nm). These calculations were performed in Wolfram Mathematica software environment and by transfer matrix method.