The paper describes the results of investigation of linear and nonlinear-optical characteristics as well as the radiation stability for biaxial LiInS2 crystal. The Sellmeier equation coefficients for the spectral range of 0.45-11.5 mkm and the values of coefficients of a nonlinear susceptibility tensor are determined. Calculations have been carried out of phase-matching conditions for different problems in the frequency conversion, namely, angular and frequency tuning dependences. A possibility has been demonstrated of realizing group matching in a wide range of wavelengths when generating the sum and difference frequencies. The paper describes the spectral dependences of group-velocity matching calculated in a direction of phase matching, whence a possibility of creating frequency converters of 3 mkm femtosecond lasers follows.