Abstract: This application relates to micelle-forming poly(ethylene oxide)-block-poly(ester) block copolymers having reactive groups on both the poly(ethylene oxide) block and the poly(ester) block therein. The biodegradability of these copolymers and their biocompatibilities with a large number of bioactive agents make them suitable as carriers for various bioactive agents. The bioactive agent, such as DNA, RNA, oligonucleotide, protein, peptide, drug and the like, can be coupled to the reactive groups on the polyester block of the copolymer. A variety of targeting moieties can be coupled to the reactive group on the poly(ethylene oxide) block for targeting the bioactive agent to a particular tissue. The application also relates to a composition and method of use thereof for delivering bioactive agents.