Lipases and proteases from various sources were tested in aromatic polyester synthesis in organic solvents. A commercial protease from Bacillus licheniformis efficiently catalyzed the transesterification of a diester of terephthalic acid and 1,4-butanediol in anhydrous tetrahydrofuran (THF). This protease was used as a catalyst in the synthesis of aromatic polyesters in THF. Oligomers with average molecular weights from 400 to 1000 daltons were obtained using various diols and aromatic diesters.