(1 -> 4)-2-Amino-2-deoxy-beta-D-glucan (i.e., chitosan) is an abundant natural polysaccharide with huge availability and potential for biomedical applications due to its biocompatibility, biodegradability, and bioactivity, but its utilization in pharmaceutical formulations has been greatly limited by its intractability. We report here a novel, facile method of controlled modification of chitosan under gamma-ray irradiation for drug delivery. Specifically, N-(2-hydroxyethyl)prop-2-enamide (HEPE) was grafted onto chitosan via a "one-pot" reversible addition fragmentation chain transfer process under gamma-ray irradiation, and then the unprotected amino group on chitosan was straightly used for the conjugation of chromone-3-carboxaldehyde. Importantly, there are no traditional protection-deprotection processes for amino groups of chitosan in this method. The conjugated graft copolymer can self-assembly into the micelles with the size of similar to 170 nm in distilled water, and the chromone release profile shows the graft copolymer could be used as a pH- and thermo-responsive carrier for drug delivery.