To provide a polyester resin composition with excellent transparency, heat resistance and impact resistance by incorporating with a polyester having diol units with a cyclic acetal skeleton, a polyester having a cyclic acetal skeleton and having less diol units than the former polyester.

The polyester resin composition is produced by incorporating (A) a polyester resin including dicarboxylic acid units and diol units with 25-60 mol% of the diol units having a cyclic acetal skeleton, with (B) a polyester resin including dicarboxylic acid units and diol units with 5-24 mol% of the diol units having a cyclic acetal skeleton so that the composition exhibits improved transparency, heat resistance and impact resistance, and is used in a wide range of fields such as sheets and injection molded moldings.