Polymer microspheres with mercapto groups were synthesized by polycondensation of 1,6-dibromohexane and 1,3-propanedithiol in the presence of a polystyrene latex and a nonionic surfactant. The sulfur content of the obtained particles is comparable with the one calculated according to the feed ratio, which shows that the polycondensation proceeds quantitatively in the particles. A higher molar ratio of dithiol against dibromide used in the polycondensation results in microspheres with higher mercapto group content.