The synthesis of poly(beta-alanine) by Candida antarctica lipase B immobilized as novozyme 435 catalyzed ring-opening of 2-azetidinone is reported. After removal of cyclic side products and low molecular weight species pure linear poly(beta-alanine) is obtained. The formation of the polymer is confirmed with H-1 NMR spectroscopy and MALDI-TOF mass spectrometry. The average degree of polymerization of the obtained polymer is limited to DP=8 by its solubility in the reaction medium. Control experiments with beta-alanine as substrate confirmed that the ring structure of the 2-azetidinone is necessary to obtain the polymer.