The mono-dispersed colloids of poly(styrene-methyl methacrylate-3-sulfopropyl methacrylate

potassium salt) P(St-MMA-SPMAP) were prepared with soap-free emulsion copolynmrization usinge a one-step or two-step method．The particle size decreases with increasing the SPMAP amount mainly due to the formation of more nucleus at higher concentration of SPMAP．Although homogeneous latex with narrow particle size dispersion can be obtained with the one-step method

the colloids prepared with this method are difficult to use in preparation of colloidal crystals because of heavy aggregation of the colloids．The two-step method can resolve this problem

the colloids prepared do not show any aggregation and are suitable to the preparation of colloidal crystals．A homogeneous nucleation is realized when the concentration of water．soluble monomer．SPMAP．is 1ess than 17mmol·dm-1 If 3-sulfooetyl-methacrylate

sodium salt (SOMAS) is used instead of SPMAP the mechanism of the emulsion polymerization becomes rather complex

because the SOMAS will play a role of emulsion agent and in this case the mono-dispersed colloids are difficult to be prepared．In this article the preparation of poly (styrene-methyl-methaerylate-3-sulfooctyl-methacrylate

sodium salt)P(St-MMA-SOMAS) colloids using a one-step method is also reported preliminary．