Disclosed herein are pH- and temperature-sensitive block copolymer with excellent safety and a method for preparing the same and a hydrogel and a drug carrier using the block copolymer. According to the present invention, the pH- and temperature-sensitive block copolymer comprises: obtained by copolymerization of: (a) polyethylene glycol-based compound (A)； and (b) poly (β-amino ester)-based oligomer (B) or poly (amido amine)-based oligomer (C) or coupling of mixture (D) thereof. In order to control biodegradation rate, the block copolymer is mixed with poly (amido amine)-based oligomer instead of the poly (β-amino ester)-based oligomer and then coupling them.
