Preparation and an aliphatic polyester resin composition of the aliphatic polyester resin

It has a high molecular weight, in a preferred embodiment, has a high melting point, thermal stability and the aliphatic polyester resin excellent in hue, and provides a process for producing it efficiently. A sulfonic acid group-containing compound as a catalyst, the melt polymerization step and a production method of aliphatic polyester containing a solid-phase polymerization step that follows, the addition of the sulfonic acid group-containing compound during melt polymerization, raw material sulfur atom in terms a monomer compared 300～3000Ppm, the content of the solid phase polymerization after the sulfonic acid group-containing compound is a polymer produced compared 300～3000Ppm sulfur atom terms, and the residual ratio of the sulfonic acid group-containing compound after solid phase polymerization production method of the aliphatic polyester resin is but 50 percent. Further, in the aliphatic polyester resin, an aliphatic polyester resin composition of the produced polymer compared 300~3000ppm containing a sulfur atom in terms of sulfonic acid group-containing compound having two or more sulfonic acid groups in one molecule.