To provide a polyester monofilament for racket strings, configured to exhibit high resilience and abrasion durability unlike a conventional polyester monofilament for racket strings, to have excellent coatability due to low heat-shrinkability, to change resilience by changing a resin composition ratio, and to be adapted to a wide range of play styles.

This polyester monofilament for racket strings is formed of a polyester resin composition comprising a polyethylene naphthalate component of 25-75 wt.% and a polyethylene terephthalate component of 25-75 wt.%. In the polyester monofilament for racket strings, a Young's modulus and a reciprocated abrasion number in a flexure abrasion test satisfy specific numerical values.