A polyvinyl acetal resin for a heat-developable photosensitive material capable of preventing skinning in the coating process of the photosensitive layer of the heat-developable photosensitive material, preventing deterioration of image characteristics and coloration of the coating solution, and suppressing the occurrence of odor at the time of producing the heat-developable photosensitive material and heat development.The polyvinyl acetal resin for a heat-developable photosensitive material used for a photosensitive layer of the heat-developable photosensitive material has a residual acetyl group content of 25 mol % or less, residual hydroxyl group content of 17-35 mol %, and polymerization degree of 200 to 3,000, and is obtained by an acetalization of a polyvinyl alcohol mixture containing polyvinyl alcohol resins having different polymerization degrees, wherein the content of the polyvinyl alcohol having a polymerization degree of 600 or less is 50 wt % or higher in the polyvinyl alcohol mixture.