Anionic copolymerizations of several bicyclic and spirocyclic bis(gamma-lactone)s (1 and 2) with various epoxides (3) were carried out at 120 degrees C in tetrahydrofuran in the presence of potassium tert-butoxide (4 mol%) as the anionic initiator. The copolymerizations of bicyclic bis(gamma-lactone)s 1 (7-substituted 1,6-dioxabicyclo[3.3.0]octa-2,5-diones) with glycidyl phenyl ether (3a) smoothly proceeded regardless of the structure of the substituent at the 7-position of 1 to give corresponding copolymers (4) in 44-78% yield. The structures of 4 were determined as the alternating copolymers by their IR and H-1 and C-13 NMR spectra. The copolymerization of spirocyclic bis(gamma-lactone) 2a (1,6-dioxaspiro[3.3]octa-2,7-dione) with 3a was sluggish but was accelerated by addition of a crown ether (8 mol%) to the polymerization system to yield the alternating copolymer 5aa in 80% yield. The copolymerization of 2b (dibenzo derivative of 2a) with 3a gave 81% yield of the alternating copolymer 5ba in the absence of the crown ether. The copolymerizations of 1 or 2 with a variety of epoxides 3 were carried out, and the effect of the structure of 3 was examined. As a result, both the steric hindrance and polarity of 3 were suggested to influence the rate of the copolymerization. Thermal properties such as glass transition and 10% weight loss temperatures of the alternating copolymers 4 and 5 were evaluated by DSC and TGA.