Phosphorus induced Na5SmSi4O12-type sodium superionic conductors were prepared by sol-gel processes with metal alkoxides. The formation region of Na5SmSi4O12-type materials was different from that of grass-ceramics. The ionic conductivities of the sol-gel-derived samples were equal to those of the glass-ceramics in the order of 10(-2)-10(-1) S/cm at 300 degrees C. The sample with the Na3.75Sm0.75Si3O9 composition sintered at 1000 degrees C for 12 h showed the highest ionic conductivity of 4.82 x 10(-2) S/cm at 300 degrees C. The grain sizes of the specimens were 3-6 mu m and the grain growth was promoted as sintering time increased.