Two important effects of the addition of Mo to the laser material CaWO4:Nd have been found and are discussed: (1) an increased susceptibility to photolytic coloring, and (2) a drastic change in the vacuum reduction coloring spectra. Therefore, it is necessary to specify the Mo concentration in CaWO4:Nd crystals in order to understand either photolytic or reduction processes. The Mo content in the crystals has been obtained from x‐ray and optical fluorescence analysis. The distribution coefficient of Mo in CaWO4 has been determined to be 0.7 from crystal growth studies. The Nd concentration is obtained in terms of the optical absorption cross sections for the 580 and 740 mμ absorption peaks. For these two wavelengths, the extraordinary ray cross sections are 10 and 2.6×10-20 cm2; the ordinary ray cross sections are 8.0 and 1.6×10-20 cm2.