To provide a polyester and fibers having high moisture-absorbing characteristics while maintaining excellent characteristics of polyester.

The copolyester is obtained by copolymerizing, to a polyethylene naphthalate resin including a dicarboxylic acid component mainly composed of naphthalene dicarboxylic acid and a diol component mainly composed of ethylene glycol, a hydrophilic compound in an amount of 10-50 wt.% relative to the total polymer weight. The copolyester has a glass transition temperature (Tg) of 50-100°C. Fibers including the same are also provided.