Poly(2-hydroxyethyl methacrylate-co-N,O-dimethacryloylhydroxylamine) particles were prepared by dispersion polymerization in toluene/2-methylpropan-1-ol medium using cellulose acetate butyrate and dibenzoyl peroxide (BPO) as a steric stabilizer and initiator, respectively. The particle size was reduced with decreasing solvency of the reaction medium (more nuclei were generated) because the critical chain length of the precipitated oligomers decreased with an increasing toluene content, which is a poorer solvent for the polymer than 2-methylpropan-1-ol. There is an optimum initiator concentration (2 wt % BPO relative to monomers) for producing low-polydispersity particles under given conditions. Additionally, discrete spherical particles were obtained at a low monomer oncentration and/or higher polymerization temperature.