PURPOSE: To obtain excellent printability and to improve the plasticizer resistance, oil resistance, solvent resistance and water resistance by using specific modified PVA resin for a thermosensitive color developing layer, a protective layer and an undercoating layer.

CONSTITUTION: Polyvinyl alcohol (PVA) polymer which contains 0.1 to 20mol% of ethylene unsaturated dicarboxylic acid monoamide or its salt as copolymer ingredient contains PVA resin represented by a formula I in the amide ingredient of ethylene unsaturated dicarboxylic acid monoamide or its salt. When the PVA resin is used as processing agent of a thermosensitive color developing layer, a protective layer and an undercoating layer of a thermosensitive recording sheet, the printability is excellent. Further, when it is used for the color developing layer and the protective layer, plasticizer resistance and oil resistance can be improved. A formula II indicates R0 of the formula I, and in the formulae I and II, n is 1 to 3, R1 to R3 are hydrogen, alkyl group or aryl group, two or more are simultaneously not hydrogen in the R2 to R3, and the total number of carbons of the R1 to R3 is 4 or more.