A polyether ester elastic fiber comprising a polyether ester elastomer containing polybutylene terephthalate as a hard segment and polyoxyethylene glycol as a soft segment and copolymerized with a specific metal organic sulfonate, having a coefficient of moisture absorption of not less than 5% at 35° C. and at a RH of 95% and a coefficient of water absorption extension of not less than 10%. The above-mentioned polyether ester elastic fiber has a good moisture-absorbing property, and is reversibly largely expanded or contracted by the absorption or release of water. Therefore, a fabric giving excellent comfortableness can be obtained from said elastic fibers, and can be recycled.