The present invention relates to biodegradable polyester resin, wherein the ratio (X/Y) of the number (X) of the first repeat unit comprising a first diol residue and an aromatic dicarboxylic acid residue to the number (Y) of the second repeat unit comprising a second diol residue and an aliphatic dicarboxylic acid residue is 0.8 to 3.0, and the impact strength index is 2.2 or more, and to a process for preparing the same. The biodegradable polyester resin can further enhance the impact absorption energy and hardness as compared with conventional biodegradable resins. Further, it can provide a biodegradable polyester film or molded article that is excellent in impact resistance, durability, and formability, along with biodegradability. Thus, it can be utilized in more diverse fields.