Solid electrolytes in the system Li2S-P2S5 are attractive for all-solid-state lithium batteries since the electrolytes have high lithium ion conductivities and wide electrochemical windows. In particular, the 75Li(2)S center dot 25P(2)S(5) (mol%) glass showed the highest stability to moisture in the system Li2S-P2S5 because the amount of H2S gas generated from the glass was the smallest in the system Li2S-P2S5. In this study, several additives such as metal sulfides and metal oxides (FeS, CuO, etc.) were mixed with the 75Li(2)S center dot 25P(2)S(5) glass in order to suppress H2S gas generation from the sulfide glasses in air. The addition of more than 30 mol% FeS greatly decreased H2S gas generation from the sulfide glass in air. In the case of the FeS addition, sulfur crystal was precipitated and the 75Li(2)S center dot 25P(2)S(5) glass changed to Li3PO4 crystal after a reaction with water. On the other hand, the addition of 30 mol% CuO dramatically decreased H2S gas generation from the sulfide glass in air. In the case of the CuO addition, Cu3PS4 crystal was precipitated after the reaction with water. Furthermore, the 75Li(2)S center dot 25P(2)S(5) glass added with 30 mol% FeS or CuO showed relatively high conductivities of more than 10(-4) S cm(-1) at room temperature. Therefore, the 75Li(2)S center dot 25P(2)S(5) glass added with FeS or CuO was expected to be a suitable solid electrolyte material for all-solid-state batteries.