The usefulness of dimethyl-, diethyl-, dibutyl- and dioctyltin oxide for the preparation of syndiotactic poly(beta-D,L-butyrolactone) was studied. Most polymerizations were conducted in bulk and :I few polymerizations in toluene or chlorobenzene. The reaction temperature was varied between 50 and 100 degrees C. Below 50 degrees C the initiatiors were not reactive enough. Me2SnO proved to be the least reactive initiator. High yields and the highest molecular weights (M-n’s up to 80 000 and M-w up to 130 000) were achieved with Bu2SnO. These high molecular weights were obtained at low monomer/initiator ratios (M/I = 50-400). In contrast to literature data, no conversion was observed at M/I ratios >600 regardless of the reaction conditions. The highest percentage of syndiotactic diads (72%) resulted either from polymerizations with Bu2SnO at 50 degrees C or with Et2SnO at 100 degrees C. Transparent films with high expansibility were cast from the 63 and 70% syndiotactic polybutyrolactone samples, which may be useful as biodegradable packaging materials.