A process for producing an aliphatic polyester through the ring-opening polymerization of a cyclic ester, wherein at least a late stage of the polymerization is caused to proceed as a solid-phase polymerization reaction and the aliphatic polyester yielded is subjected to a step for removing the residual cyclic ester to a gas phase. Thus, an aliphatic polyester can be obtained in which the contentof the residual monomer has been minimized.