The present disclosure relates to a polypeptide based block copolymer having biodegradability due to peptidase, and a process for the preparation thereof, and polymer micelles using the same. The block copolymer according to the present disclosure is a block copolymer of a polyethylene glycol-based compound having properties such that the solubility for water is different depending on the pH, but cannot form micelles due to a self-assembly phenomenon; and a polyglutamic acid-based compound formed using an aminolysis reaction of glutamic acid and tertiary amine in which the end of one alkyl group is substituted with NH2, or using an aminolysis reaction of glutamic acid and triamine. The block copolymer of the present disclosure has advantages in that the block polymer has both pH sensitivity and biodegradability due to peptidase in the body, and thereby a degradation rate related to a drug release cycle is controlled. Therefore, the block copolymer according to the present disclosure is effective in that the block copolymer can be used as a target-oriented drug delivery agent depending on the pH changes in the body, and as a drug delivery agent that can control the rate of degradation.