Sulfide solid electrolytes with cubic Na3PS4 phase were firstly synthesized via a liquid-phase process. A yellow solution was obtained after the reaction of Na2S and P2S5 in N-methylformamide (NMF) solvent, and a cubic Na3PS4 was mainly precipitated by heat treatment for removing the solvent. The ionic conductivity of the obtained electrolyte was 2.6 x 10(-6) S cm(-1) at room temperature. The present conductivity is not as high as a Na+ ion conductor, but the prepared solution is useful for forming an electrolyte coating on electrode particles, Which will improve the electrochemical performance of all-solid-state sodium batteries.