Optical absorption and magnetic susceptibility data of the Zn1-xMnxGa2Se4 family of compounds have been collected in the temperature range 10–300 K. One of the most interesting aspects of this series is the availability of samples in the whole composition range, in contrast with most diluted magnetic semiconductors that are only miscible in a limited range of compositions. Temperature-independent absorption bands with maxima at 2.33, 2.49, and 2.66 eV have been found that are assigned to electron transitions from the 6A1 ground state to the 4T1, 4T2, and 4A1, or 4E excited states of the Mn++ ion in a tetrahedral crystalline field. The optical spectra exhibit a temperature dependent absorption edge in the 350–600 nm region that corresponds to a direct band gap. The band gap energy has been determined as a function of atomic concentration and temperature. At room temperature, the variation of the energy gap Eg with the Mn content shows a rather anomalous behavior that consists of an initial decrease for x≪0.1, followed by a roughly flat variation for 0.1≪x≪0.5, and a nearly linear increase for x≫0.5. An analogous evolution of Eg with x is found when decreasing temperature. Such behavior has been compared with that reported for analogous systems. The variation of Eg with temperature follows Varshni’s relation for all compositions. A monotonic increase of the magnetic susceptibility with x is found within the whole range of Mn content- . © 2001 American Institute of Physics.