The sulfide solid electrolytes have the characteristics of high ionic conductivity and low grain boundary resistance, which make them suitable for bulk-type all-solid-state batteries. However, most of them suffer from poor stability in air. Here, we explore the air stable sulfide solid electrolytes in Li4SnS4-Li3SbS4 system. The solid solutions of Li4– x Sb x Sn1– x S4 (0 ≤ x ≤ 0.5) can be formed in Li4SnS4-Li3SbS4 system. Li3.8Sb0.2Sn0.8S4 achieves the highest ionic conductivity of 3.5 × 10−4 S cm−1 in this system, which is 5 times as that of Li4SnS4 and 3 orders of magnitude higher than that of Li3SbS4, respectively. Li3.8Sb0.2Sn0.8S4 crystallizes into the same structure with high ionic conductivity phase of β-Li3PS4. Moreover, Li3.8Sb0.2Sn0.8S4 owns good stability in humid air. Matching with LiCoO2 and Li4Ti5O12, Li3.8Sb0.2Sn0.8S4 exhibits the potential to be applied in all-solid-state batteries.