To provide a polyester conjugate monofilament particularly having characteristics as strings for rackets and the string for racket having both of the excellent ball-striking properties and the excellent surface pressure-retaining property after stretching strings which natural strings have while keeping excellent durability which the string made of a synthetic resin has.

In the polyester conjugate monofilament, a core part polymer or an island part polymer is composed of polypropylene terephthalate and a sheath part polymer or a sea part polymer is composed of polyethylene terephthalate.