Capacitive-type humidity sensors were prepared using four kinds of polymerized vinyl carboxylate, i.e., vinyl benzoate, vinyl methacrylate, vinyl crotonate and vinyl cinnamate. These monomers have different chemical structures and vinyl methacrylate and vinyl crotonate formed a cross-linked film. The sensitivity was enhanced by proceeding the cross-linking reaction. This is due to the increase in the water sorption ability The temperature coefficient of the sensitivity decreased by using the cross-linked polymer. Although the electrical capacitance of all sensors was affected by acetone vapor, the capacitance of the cross-linked sensor recovered to the initial value after removal of the acetone vapor. The cross-linking technique was effective for forming a rigid film which prevents the swelling of the polymer in the acetone. vapor. The present cross-linked humidity sensor is suitable for practical use.