The phase equilibriums in the AgInS2-CuInS2 system were investigated by means of X-ray diffraction and differential thermal analysis and the AgInS2 and CuInS2 ternary compounds and the AgxCu1-xInS2 solid solutions were grown by two-zone horizontal method with the following directed crystallization of melt. The T-x phase diagram of this system was constructed and the formation of solid solutions in the complete range of compositions was discovered. The composition dependencies of microhardness, transmission spectra in the range of the fundamental absorption, infrared transmission spectra in the range from 150 to 400 cm(-1) for the AgxCu1-xInS2 solid solutions were investigated. It was discovered that the composition dependence of microhardness is expressed by smooth curve having maximum for x=0.2. The composition dependencies of band gap have been analytically expressed at 77 and 293 K for the E perpendicular to c and E parallel to c direction of polarization and have non-linear behaviour. EE From the studies of the infrared transmission spectra the frequencies of optical phonons were determined and it was discovered that their composition dependence shows single mode behaviour.