PURPOSE: To obtain a humidity sensor which facilitates extraction of signal changes with a characteristic of allowing capacitance to vary almost linearly on a logarithmic graph by using cyanoethylcellulose for the humidity-sensitive film.

CONSTITUTION: A cyanoethylcellulose flake with a substitution degree of 2 and 5 and a polymerization degree of 250 is dissolved into dimethylformaldehyde to be a 30% solution and 10wt% of BaTiO3 is added to the solution with respect to ethylcellulose flake and kneaded to form a paste, which is applied on a substrate side electrode 1 to form a humidity-sensitive film 2 while an electrode 3 is formed to make a humidity-sensitive sensor. The cyanoethylcellulose is obtained by reacting cellulose upon excessive acrylonitrile under an alkali catalyst. When the substitution degree of the cyanoethyl group is below 2.0, no sufficient dielectric can be obtained and when it exceeds 2.8, the hygroscopicity is so poor as to achieve no sufficient humidity sensitivity.