A small-angle X-ray scattering (SAXS) study of a model copolymer latex, composed of styrene and pentabromobenzyl acrylate (PBBA, 40 wt %), is presented. The contrast variation method employed in this study was shown to be a sensitive probe for inhomogeneity in the particles. The separation of the homogeneous function allows direct calculation of the size distribution of the spherical particles (volume average diameter, 26.7 +/- 1.3 nm). The SAXS analysis reveals a particle’s inner structure described as a continuos copolymer phase, of composition being slightly richer in PBBA, within which domains of polystyrene are randomly distributed. The volume fraction of the polystyrene domains was estimated as 11 vol % and their characteristic length as 5.1 nm.