Abstract: Disclosed is a method for preparing a biodegradable polymer in the form of uniform powder or spherical particles by dispersion polymerization without a grinding step. The method for preparing a biodegradable polyester includes dispersing a monomer in the presence of a catalyst in a dispersion solvent to form a solid or liquid phase for dispersion polymerization and thereby to yield a biodegradable aliphatic polyester in the form of spherical particles or powder, the monomer comprising a mixture of a first compound (e.g., lactide or glycolide) and a second compound being selected from the group consisting of polyhydric alcohols (e.g., glycerin, erythritol, penterythritol or dipentaerythritol) and carprolactone. The present invention readily prepares a biodegradable polymer having a high molecular weight in the form of uniform powder or spherical particles.