The present invention relates to a biodegradable polyester resin, in which the first repeat unit comprising a first diol residue and an aromatic dicarboxylic acid residue and the second repeat unit comprising a second diol residue and an aliphatic dicarboxylic acid residue satisfy a ratio of the number of repeat units in a specific range, and the softness index of the resin satisfies a specific range, and to a process for preparing the same. Since the biodegradable polyester resin can provide a biodegradable polyester sheet or film that can be simultaneously enhanced in productivity, processability, and moldability and is excellent in tensile strength, tear strength, and friction coefficient and excellent in biodegradability and water degradability, it can be utilized in more diverse fields.