The self-assembly behavior of poly(gamma-benzyl-L-glutamate)-graft-poly(ethylene glycol) rod-coil graft copolymers in aqueous solution was investigated. With tetrahydrofuran (THF) as initial solvent, vesicles were observed for the graft copolymers with lower degree of grafting. When the degree of grafting increases, the aggregate morphology transforms from vesicles to spindle-like micelles then to spherical micelles. When N,N'-dimethylformamide (DMF) is introduced into the initial solvent, the vesicles transform to spindles. Increasing DMF volume fraction leads to it spindle to connected-spindle transition. On the basis of the experimental results, the mechanism of the morphological transition of the rod-coil graft copolymer is suggested.