To provide a new indolyl phthalide polymer and a new indolyl phthalide copolymer, and to provide a heat-sensitive recording material using them, giving good cyan-color images and slight in photostaining on the white background.

The indolyl phthalide polymer is represented by the general formula (1). The indolyl phthalide copolymer is obtained by copolymerization between a monomer of the general formula (2) and a monomer having an ethylenically unsaturated double bond. The heat-sensitive recording material using them is also provided. In the general formula (1) and the general formula (2), R1 is H or an alkyl; R2 is an alkyl or aryl; R3 and R4 are each H, an alkyl or aryl; Z is a single bond or bivalent group; Y1, Y2, Y3 and Y4 area each CH, or one or two of them is (are each) N, the other being each CH; and in the general formula (1), n is 2-200.