The comparison of organolanthanide complexes, (C5Me5)(2)SmMe(THF) (Sm1) and [(C5Me5)(2)SM](2)(PhC=C= C=CPh) (Sm2), with tin compounds, Bu2Sn(OMe)(2) (Sn1) and Bu2Sn(OCH2CH2CH2O) (Sn2), in the preparation of random and diblock copolymers composed Of L-lactide (L-LA) or D,L-LA and F-caprolactone (CL), and the preparation of triblock copolymers composed Of L-LA/CL/L-LA was studied and the biodegradabilities of the resulting copolymers with proteinase K and a compost were examined. Poly(L-LA-ran-CL) shows much higher degradability than poly(L-LA) with proteinase K, and poly(L-LA), poly(L-LA-ran-CL) and poly(L-LA-b-CL) (b means block) prepared with Sm1 had better degradability than those synthesized with the Sn1 compound. The degradability Of Poly(L-LA-ran-CL) with proteinase K is higher than that Of poly(L-LA-b-CL). Poly(LA-ran-CL) and poly(LA-b-CL) prepared with Sml revealed higher degradability than those obtained with Sn1 using a compost. Triblock copolymers, poly(L-LA-b-CL-b-L-LA), synthesized with Sm2 revealed nearly the same degradability with those obtained with Sn2 using a compost. Finally, biocompatibility was studied with macrophage activation assay using RAW 264.7, and metabolic viability assay using Cell Titer Aqueous non-radioactive Cell. (C) 2004 Elsevier B.V. All rights reserved.