The functionalized core-shell monodisperse latex particles with surface chloromethyl groups were synthesized by means of a two-step emulsion polymerization process in a batch reactor at two reaction temperatures. In a first step, the core was synthesized by means of a batch emulsion polymerization of styrene (St), and in the second step, the shell was formed bg batch emulsion copolymerization of St and (chloromethyl)styrene (CMS) using the seed obtained previously. The latexes were characterized by TEM and conductopotentiometric titrations in order to obtain the particle size distribution and the amount of the different surface groups, respectively. Covalent binding of protein to chloromethyl groups was studied using lysozyme at two pHs, 7 and 11. Two different methods were used to determine the amount of protein covalently bound or physically adsorbed : desorption with surfactants, and chloride ions release upon chemical binding.