Lasing parameters, optical absorption, fluorescent properties, and laser‐damage threshold were studied in samples of an Nd‐doped Ca‐Mg silicate glass which were phase‐separated to various degrees. The phase‐separation process was followed by low‐angle X‐ray scattering and electron microscopy. Lasing efficiencies increased when small amounts of phase separation were present, but in general efficiencies decreased and laser thresholds increased with increased phase separation. Optical absorption was essentially unchanged except for scattering at the shorter visible wavelengths. Fluorescent lifetimes and integrated intensities were virtually unchanged by various heat treatments. Laser‐radiation‐damage thresholds appeared to increase slightly with increased phase separation. Low‐angle X‐ray scattering showed that the particle size increased continuously with increasing heat‐treatment time, although the number density of particles decreased initially.