The effect of polystyrene (PS) homopolymer on the diameter of mieelles self-assembled by polystyrene-b-poly(acrylic acid) (PS-b-PAA) in water was studied by dynamic laser light scattering and transmission electron microscopy．The results show that polystyrene can take part in the self-assembly of block copolymer PS-b-PAA in water and forms part of the core of the resulting core-shell micelles due to the affinity between the PS homopolymer and the PS block．because their structures are the same．The mieelles are generally inonodisperse when the content of the PS homopolymer is in a given region

as well as its molecular weight．Besides

it is also found that the size of the micelles can be controlled conveniently by adjusting the content and the molecular weight of the PS homopolymer The hydrodynamic diameter of the mieellels inereases from 60 nm to 95 nm as the weight ratio of the PS homopolymer to the PS block is inereased from 1/1 to 4/1．and inereases from 60 nm to 120 nm as the molecular weight ratio of the PS homopolymer to the PS block increases from 1/2 to 4/1．