57 This invention relates to a water resistant composition which comprises (A) polyvinyl alcohol, (B) a chitosan, the aqueous 1% solution of which has a viscosity not greater than 70 centipoise at 20°C, and (C) an aldehyde compound, as well as a heat-sensitive recording sheet which comprises said composition. The composition has excellent water resistant properties and the heat-sensitive recording sheet has improved color forming properties and excellent resistance to water and solvents.