A thermo-sensitve copolymer of following formula; ##STR00001## is disclosed; wherein R.sub.1 is hydrogen, or --C(.dbd.O)--R.sub.2; R.sub.2 is C.sub.7-30 alkyl substituted or unsubstituted with functional groups; R.sub.3 is hydrogen, or C.sub.1-6 alkyl; and x, y or z individually is an integer greater than 0. The thermo-sensitive copolymers disclosed here are easy to be implanted into a human body through injection. The biodegradability is greatly improved and the cytotoxicity of the copolymers is low.