Cadmium sulfide (CdS) nanoparticles and poly(methyl methacrylate) (PMMA) were first synthesized in methyl methacrylate (MMA) /sodium bis(2-ethylhexyl) sulfosuccinate (AOT) microemulsion, in which MMA acts as the solvent and monomer. Then compressed CO2 was used as an antisolvent to precipitate the CdS and PMMA simultaneously. Using this method, a CdS/ PMMA composite was successfully prepared. The CdS nanoparticles dispersed in the polymer matrices were characterized by transmission electron microscopy. The higher pressure is favorable to producing CdS nano-particles of smaller size. The phase structure of the obtained composite was characterized by X-ray diffraction, which reveals that cubic CdS particles were formed. The FTIR spectra of the composite showed that there is no chemical bonding or strong interaction between CdS and PMMA. (C) 2004 Wiley Periodicals, Inc.