The first two new Na-containing sulfides Na2In2MS6 (M = Si (1), Ge (2)) in the Na(2)Q-B(2)Q(3)-CQ(2) (B = Ga, In; C = Si, Ge, Sn; Q= S, Se) system were prepared for the first time through conventional high-temperature solidstate reaction. They are isostructural with space group Cc (No. 9) in monoclinic phases and feature three-dimensional frameworks built by the (1)(infinity)[In2MS6](2-) (M = Si, Ge) chains through corner-sharing InS4 tetrahedra and MS4 (M = Si, Ge) tetrahedra, with Na+ cation located in the cavities. They display moderate second harmonic generation (SHG) conversion efficiencies compared with commercial AgGaS2, with phase-matching behavior at 1800 nm and laser-induced damage 6.9 and 4.0 times higher than that of AgGaS2, respectively. Therefore, the output SHG intensities of 1 and 2 will be similar to 4.3 and 4.0 times larger than that of AgGaS2, when the intensity of incident laser increased to close the damage energy of 1 and 2, indicating their potential for high-power nonlinear optical application.