For polycrystalline films of MnAs the complex index of refraction, N=n—ink, and the off-diagonal component of the complex dielectric tensor, Q=Q0 exp (-iq) were determined as functions of wave-length from 0.45 μm to 0.95 μm. The complex index of refraction increases from N=1.84-i1.75 at 0.45 μm to 2.13-i3.33 at 0.95 μm. Q0 and q increase from 0.008 and 29° at 0.45 μm to a maximum of 0.0194 and 55° at 0.9 μm, respectively. The dispersion of the Kerr rotation shows a change in sign at 0.72 μm. A maximum Kerr rotation of +0.058° is found at 0.9 μm and a maximum Kerr ellipticity of −0.15° at 0.72 μm. From these data a Faraday effect | 2F | = π | NQ|/λ0 of 156 000°/cm and an absorption coefficient α=4πnk/λ0 of 4.5×105/cm were calculated at 0.8 μm. The figure of merit is f=|2F|/α=0.34°. Also calculated were the complex dielectric constant ε and the reflectivity R. A description of the film preparation technique in high vacuum (10−7 Torr) is given. The films were analysed by x-ray diffraction techniques and were found to be stoichiometric MnAs.