The optical properties, damage threshold, and thermal conductivity of a new nonlinear LiInSe2 crystal of the mm2 point symmetry group have been investigated. The transparency range of a red colored crystal is 0.4-13.5 mm at the zero level. The damage level is 248 ± 16 MW/cm2 at 30 ns pulsed ТЕА СО2 laser pump, that is, 1.7 times as high as that of ZnGeP2. The thermal conductivity is 0.014 ± 0.002 W/cm2 K. Second harmonic generation was obtained for the first time for the ТЕА СО2 laser. The energy conversion efficiency for the 9.55 mm emission line was 1.5% in energy and 2.6% in peak power at the pump intensity of 38.5 MW/cm2, and that for the 9.26 mm line was 4.3% in peak power. The second harmonic generation efficiency versus the pump angle and wavelength is presented.