PURPOSE: To obtain the subject elastic yarn having excellent elastic recovery and producible by melt-polymerization and melt-spinning by using a block copolymer composed of an aromatic polyester component and a poly(alkylene oxide) glycol component and having a specific composition.

CONSTITUTION: The aromatic polyester component constituting the hard segment of this block copolymer is composed of the recurring units of the formula I and the formula II (Ar is a 6-2OC arylene; R is 2-10C alkylene; (n) is integer of 2-12) (constitution molar ratio I:II is 100:0 to 50:50) and the soft segment accounting for 70-95wt.% of the block copolymer is composed of a poly(alkylene oxide) glycol component having a number average molecular weight of 500-3,000.