A two-stage, multistep soapless emulsion polymerization was employed to prepare various sizes of reactive core-shell particles (CSPs) with butyl acrylate (BA) as the core and methyl methacrylate (MMA) copolymerizing with various concentrations of glycidyl methacrylate (GMA) as the shell. Ethylene glycol dimethacrylate (EG-DMA) was used to crosslink either the core or shell. The number of epoxy groups in a particle of the prepared CSP measured by chemical titration was close to the calculated value based on the assumption that the added GMA participated in the entire polymerization unless it was higher than 29 mol %. Similar results were also found for their solid-state 13 C-NMR spectroscopy. The MMA/GMA copolymerized and EGDMA-crosslinked shell of the CSP had a maximum glass transition temperature ( T g ) of 140ЊC, which was decreased with the content of GMA at a rate of 01ЊC/mol %. However, the shell without crosslinking had a maximum T g of 127ЊC, which decreased at a rate of 00.83ЊC/mol %. The T g of the interphasial region between the core and shell was 65ЊC, which was invariant with the design variables. The T g of the BA core was 043ЊC, but it could be increased to 035ЊC by crosslinking with EGDMA. The T g values of the core and shell were also invariant with the size of the CSP.