The optical constants of indium phosphide (InP) in the soft x-ray region of $50–200\AA$ are determined from angle-dependent reflectivity measurements. The measurements are carried out using the reflectivity beam line at the Indus-1 synchrotron source. The derived optical constants are compared with tabulated values of Henke et al. [ At. Data Nucl. Data Tables 54, 181 (1993)]. Experimental values of δ and β are in close agreement with the tabulated values in the lower wavelength region of $50–120\AA$ . The experimental value indicates an edge shift of $0.4\AA$ toward the lower wavelength side from the phosphorous L-edge value of $92\AA$ . However, above the $120\AA$ region, where the indium ${\mathrm{N}}_2$ edge falls at $160.7\AA$ , there is a huge difference between experimental and tabulated values. Both delta and beta values are significantly higher. In contrast to tabulated values of the $\beta /\delta$ ratio, which is more than 1 above the $140\AA$ region, the experimental measured ratio is found to be less than 1. This study presents the first reported experimental values of optical constants for InP in this wavelength range, to the best of our knowledge.