The measurement of electrical conductivity (s) and Seebeck coefficient (S) of the studied solid of the system (1-x) Li3PO4 : x Li3 VO4 with x = 0, 0.33, 0.55, 0.67 and 1.0 have been reported from 500 K to melting point of the solid. All the studied solids show superionic phase just below their melting point. In superionic phase s value and activation energy decreases but the temperature span of superionic phase increases for the solids with the increase in x. The phase transition temperature (Tp) from normal to superionic phase decreases with decrease in x. All the solids are mixed conductors with dominant ionic conductivity below transition temperature Tp.