Abstract: The present invention related to a drug release controlling material responsive to changes in temperature comprising the polyester gel which is obtained by polymerization of a polyfunctional macromonomer represented by the general formula (I): ##STR1## wherein R.sup.1 represents a hydrogen atom or an alkyl group having from 1 to 6 carbon atoms, X.sup.1 represents a hydrogen atom, a halogen atom, a cyano group, an alkyl group having from 1 to 6 carbon atoms or a phenyl group, A represents an aliphatic polyester chain, m is 0 or 1, and p, which may be the same or different in each branched chain, represents an integer of from 0 to 6, optionally with a polyethylene glycol derivative which contains polymerizable group(s) at the end(s). The drug release controlling material has an on-off control function of drug release responsive to changes in temperature depending upon the gel transition of the aliphatic polyester gel.