The dependences of the integral intensity and kinetics of mid-IR cathodoluminescence (CL) of Fe:ZnSe crystals on an iron concentration varying from 0.01 to 14 wt % are studied in the temperature range from 78 to 300 K. It is found that the maximum mid-IR CL intensity in Fe:ZnSe is observed at an Fe concentration of about 2 wt % at room temperature and 0.8–1 wt % at liquid nitrogen temperature. A further increase in iron concentration leads to a decrease in the CL decay time.