A new thio-germanium sulfide Li2Ga2GeS6 has been synthesized for the first time and its structure was found to be isomorphous with AgGaGeS4, which is well-known as a promising infrared NLO material. The host structure is built of GaS4 tetrahedra linked by corners to GeS4 tetrahedra to create a 3D framework forming tunnels along the c-axis, in which the Li+ ions are located. The second harmonic generation (SHG) efficiency determined on powders of Li2Ga2GaS6 is ∼200 times larger than that of α-SiO2. Unlike AgGaS2 and AgGaGeS4, Li2Ga2GeS6 was observed to be very stable under prolonged Nd:YAG 1.064 μm laser pumping, indicative of a large improvement in laser damage threshold. This new material could supplant Ag phases in the next generation of high-power infrared NLO applications.