The effects of the swelling ratio (SIR), the existence of methyl side groups, the length and molecular structure of backbone chain of crosslinking monomer on the variation of mechanical properties of single polymer particle were investigated. For the study, monodisperse polymer particles were prepared via one-step seeded polymerization using PMMA as seed particles and 1,n-alkanediol di(meth)acrylate or (ethylene glycol)(n) di(meth)acrylate as crosslinking monomer. Recovery rate, K-values, breaking strength, and breaking displacement were measured as mechanical properties and they were performed by using microcompression test. The following observations were made: (1) only breaking strength was closely related to the swelling ratio; (2) the existence of methyl side groups increased the K-values but decreased the recovery rate of the polymer particles; and (3) K-values were the most sensitive to the variation of backbone chain length of crosslinking monomer, and they were decreased with the increase of the backbone chain length of crosslinking monomer. (c) 2007 Wiley Periodicals, Inc.