Phase-matching conditions are considered for second harmonic generation (SHG) and optical parametric generation in LiGa(S1-xSex)(2) mixed crystals as a function of chemical composition under the supposition of linear dependence of refractive indices on x. It has been shown that by tuning x over the range 0-1 the SHG can be realized in XY plane for lambda = 2.1-7.8 mu m pumping at rho = 43-90 degrees, in YZ plane for lambda = 2.1-2.2 and 4.8-7.8 mu m pumping at theta = 0-90 degrees, and in XZ plane for lambda = 1.6-11.7 mu m pumping at theta = 0-57 degrees. The LiGa(S1-xSex)(2) solid solutions are also attractive for design of tunable femtosecond pulse frequency converters with saving of pump pulse duration. (c) 2006 Elsevier B.V. All rights reserved.