Abstract: Disclosed is a block copolymer formed by coupling the following components with each other: (a) a copolymer (A) of a polyethylene glycol (PEG) type compound with a biodegradable polymer; and (b) at least one oligomer (B) selected from the group consisting of poly(?-amino ester) and poly(amido amine). A method for preparing the same block copolymer, and a polymeric hydrogel type drug composition comprising the temperature and pH-sensitive block copolymer and a physiologically active substance that can be encapsulated with the block copolymer are also disclosed. The multiblock copolymer is obtained by copolymerization of a pH-sensitive poly(?-amino ester) and/or poly(amido amine) type oligomer, a hydrophilic and temperature-sensitive polyethylene glycol type compound and a hydrophobic and biodegradable polymer.