A biodegradable polyester is formed by carrying out esterification and polycondensation with a carboxylic acid monomer group comprising at least one aliphatic dicarboxylic acid containing 2 to 14 carbon atoms and at least one aromatic or alicyclic carboxylic acid, and at least one glycol in the presence of a composite catalyst comprising a titanium compound, a zinc compound, an antimony compound and a phosphorous compound. The composite catalyst significantly improves the reaction rate of polyester polymerization as well as increases the production amounts of the polyester, as compared with conventional catalysts. The polyester is high in molecular weight, excellent in thermal and mechanical properties by virtue of the introduction of the aromatic or alicyclic carboxylic acid or its derivative, in addition to showing good biodegradability. This polyester can replace preexisting, expensive aliphatic polyesters.