Humidity sensors using various NASICON materials have been experimentally produced by the thick-film printing method. Among the NASICON materials, one which did not contain phosphorus shows a comparatively low resistance in low humidity. The relation between the logarithm of its resistance and relative humidity is almost linear and hysteresis free (2 M-OMEGA--10 k-OMEGA in the range 20-90% r.h.). Also the humidity sensor using NASICON material not containing phosphorus compared with one using usual NASICON containing phosphorus has improved long-term stability and durability in various environmental tests.