Polymeric nanospheres consisting of poly(butyl methacrylate)(PBMA) cores and poly (ethylene glycol) (PEG) branches on their surfaces were prepared by free radical copolymefization of butyl methacrylate (BMA) and PEG macromonomer with a p-vinylbenzyl end group in ethanol/water mixed medium．It was found that the solvophilidsolvophobie balance between the copolymers and mediums had great effect on the formation of nanospheres．The obtmned polymer dispersion exhibited four kinds of states：clear solution

particle dispersion (milky solution)

milky solution with gel/precipitation and gel with varying the BMA concentration and water content in the mixed medium．The particle size and morphology of obtained nanospheres were characterized by the transmission electron microscopy and laser ljghter scattering．The nearly monadispersed nanospheres with particle sizes from 40 nm to 500 nm could be obtained by eontroHing the BMA concentration and water content in mixed medium．