We have investigated Cd1−xMnxTe thin films with Mn concentrations of x=0.12, 0.18, 0.30, 0.52, and 0.70. These single crystal layers were grown by molecular beam epitaxy on  CdTe substrates. The real part of the refractive index, n, was determined below the band‐gap E0 in the range of 0.5–2.5 eV at T=300 K. The parallel reflectivity was measured near the Brewster angle at the YAG laser wavelength of 1.064 μm (hν=1.165 eV). Combining these results with the optical pathlength results (nd) of reflection measurements in a Fourier spectrometer we have determined n(x,ν) over a wide spectral range by utilizing a three parameter fit. The accuracy of these results for n should improve waveguide designs based on this material.