A new binary composite electrolyte of 3Li 4 SiS 4 –0.5La 2 S 3 was successfully prepared by mechanical milling for 10h. In the composition, Li 4 SiS 4 was mainly in amorphous phase, and La 2 S 3 kept in crystal phase. The total lithium ion conductivities at 27°C (σ 27 ) and 150°C (σ 150 ) were calculated to be 2.77×10 −4 S/cm and 1.84×10 −2 S/cm, respectively. The corresponding activation was calculated to be 38kJ/mol. And the electrochemical stability was found in a wide potential range of up to 5.5V vs. Li + /Li. For comparison, quenching technique was used to prepare the sample and the results showed that it is inferior to mechanical milling.