a biodegradable , optically active copolymer is disclosed . the copolymer is represented by general formula : ## str1 ## wherein r 1 represents a group selected from the group consisting of methyldimethylene , 1 , 2 - dimethyldimethylene , 1 , 1 - dimethyldimethylene , methyltrimethylene , tetramethylene , methyltetramethylene , pentamethylene , 1 , 4 - dimethyl - 2 - oxo - 3 - oxytetramethylene , 2 - oxo - 3 - oxytetramethylene , and 2 - methyl - 3 - oxypentamethylene , and m and n each represents a natural number of from 10 to 15 , 000 . according to the present invention , useful polymers which are a new type of functional materials characterized as having optical activity , biodegradability , and hydrolyzability can be easily produced in an industrially advantageous manner by the ring - opening copolymerization of optically active β - butyrolactone with various lactones .