Polymer microspheres with narrow size distribution and with carboxyl groups on their surfaces were synthesized by soap-free emulsion polymerization of methyl methacrylate (MMA), ethyl acrylate (EA), and acrylic acid (AA), and the distribution of -COOH in the latex was determined by conductometric titration. Effects of ingredients on polymerization, latex particle size (D-p), and its distribution, and the distribution of -COOH were investigated. Results showed that monomer conversion and the amount of embedded -COOH (E-a) decreased, and D-p increased with increasing amounts of NH4HCO3. The amounts of surface -COOH (S-d) and water -COOH (F-n) and the number of -COOH on each square centimeter of the particles' surface (S-d) increased with increasing amounts of NH4HCO3 and AA. With the increase of initiator (APS) and AA, DP deceased. E-a increased with the increase of AA. F-a increased and then remained constant, and S-d decreased with the increase of initiator. (C) 2004 Wiley Periodicals, Inc. J Appl Polym Sci 92: 433-438, 2004.