[en] Single crystals of CuGaS₂, CuInS₂ and their solid solutions CuGasub(1-x)Insub(x)S₂ of whole range are grown from In solution. Iodine vapour transports of these crystals are also carried out. The lattice constants ''a'' and ''c'' change almost linearly with the composition x, i.e., obey Vegard's law. Reflection, transmission and photoconduction are measured at 300K and 110K using the polarised light. From the results of reflection and transmission measurements, it is confirmed that CuGaS₂ has two closely spaced valence bands (the higher one is for E parallel to Z and the lower one is for E perpendicular to Z), and CuInS₂ has one degenerated valence band (no polarisation effect). As the composition x is changed from 0 to 1, the separation of the two valence bands is going to be smaller and finally degenerated into one band. This behaviour shows directly that the separation is attributed to the crystal field splitting. In photoconduction, more one band which is always separated from the other two bands is observed mainly for E perpendicular to Z, though any assignment is not made for this new band. Composition dependences of the energy gaps change almost linearly. (auth.)