To provide a novel high-molecular-weight aliphatic polyester that is short in reaction time required until the polyester, has a sufficiently high molecular weight and is excellent in biodegradability and to provide an industrially advantageous process for producing the polyester.

The biodegradable high-molecular-weight aliphatic polyester comprises an ester part A represented by formula (1) (wherein R1 denotes a 1-12C divalent aliphatic group; R2 denotes a 2-12C divalent aliphatic group; and p denotes a molar fraction of the ester part represented by formula (1) contained in the polyester) and an ester part B represented by formula (2) (wherein R1 denotes a 1-12C divalent aliphatic group; R3 denotes H or a polyester residue; and r denotes a molar fraction of the ester part represented by formula (2) contained in the polyester) wherein the value of the molar fraction r of the ester part B is in the range of 0.001-0.10.