The pressure and wavelength dependence of refractive indices of amorphous As2S3 have been studied by means of observing transmission light interference spectrum under room temperature with the high-pressure microspectroscopic system in conjunction with the gasketed diamond anvil cell, in which methanol-ethanol mixture was used as pressure liquid with hydrostatic pressure up to 66kbar and wavelength between 400-900 nm. The pressure was monitored by ruby R-line shift. Amorphous As2S3 thin film samples a few micrometers in thickness were prepared by vacuum evaporation. Under our experimental conditions, neither the light of 441.6 nm He-Cd laser used for excitation of the ruby gauge, nor that of the Br-W lamp for measurement of light transmission, showed any detectable influence on the optical properties of the sample.By observing the interference maxima at energies below the absorption threshold and using the results of. Gerlich et al. of the pressure dependence of volume of a-As2S3, the pressure dependence of refractive index between 500-850 nm have been determined. The refractive index of amorphous As2S3 is significantly pressure-sensitive, increasing by 35% at 650 nm with pressure change of 66 kbar. Analysis of experimental data by least-square method on the computer gives the coefficients of the nonlinear formula n(p)=n(0)+Ap+Bp2, where n(p) and n(0) are refractive indices at pressure p and 1 bar, respectivelly; coefficients A and B are relative to wavelength, for example A=9.62×10-3 kbar-1,B=2.07×10-3 kbar-2, for wavelength) λ = 800nm and other values were given in the paper. This relationship is different from the results of Weinstein et al. and Galkiewicz et al., where linear relationship between n and p at fixed wavelength in infra-red regime was reported. The difference, however, may be attributed to the different method of sample preparation etc.