Unimacromolucule exchange between bimodal star micelles self-assembled by polystyrene-block-poly(acrylic acid) and poly styrene-block-poly(amino propylene-glycol methacrylate) in water has been studied by laser light scattering. Unimacromolucule exchange can take place in the mixture of the bimodal star micelle aqueous solution at 25 degreesC. Increasing temperature accelerates the rate of the unimacromolucule exchange. The unimacromolucule exchange between the bimodal star micelles is proved by the changes of the hydrodynamic radius (R-h) the gyration radius (R-g), and the R-g/R-h value of the mixed bimodal star micelles when the mixed bimodal micelle solution is heated at different temperatures. The reason for unimacromolucule exchange between the "frozen" bimodal star micelles is discussed, and a possible mechanism is suggested. The unimacromolucule exchange results in the formation of hybrid micelles with a more compact structure than that of typical star micelles due to the strong affinity between the functional groups in the shell-forming blocks of the copolymer chains.