Abstract: Disclosed herein is a paper coating agent which comprises a modified polyvinyl alcohol (A) containing 3 to 15 mol % of ethylene units and an alkali metal ion (B), with the ratio of component (A) to component (B) being 100:0.003 to 100:1 in parts by weight. Disclosed also herein is a heat-sensitive recording material which comprises a coating layer on a substrate, said coating layer comprising a modified polyvinyl alcohol containing 3 to 15 mol % of ethylene units.The paper coating agent of the present invention has such excellent solubility in boiling water that there is not a problem of insoluble matter in an aqueous solution of the coating agent. When applied for a paper surface coating agent, it gives coated paper without discoloration, superior, in surface strength, air barrier properties, and printability. When applied for a paper pigmented coating agent, it gives coated paper without discoloration, superior in water resistance and printability.