Epoxy resin (Ep850)/acrylic composite latex was prepared by the miniemulsion polymerization method. Epoxy-functionalized latex made by the miniemulsion polymerization process with Ep850 was, compared with that made by the conventional emulsion polymerization process with glycidyl methacrylate (GMA). The reactivity and stability of epoxy groups were investigated in the latexes and films, and quantified by Fourier transform-IR spectrometry. The solvent resistance of films strongly correlated with the residual epoxy groups in latex. The epoxy groups originating from Ep850 in the miniemulsion process were less reactive than those from GMA in the conventional process. Almost all epoxy groups originating from Ep850 in the miniemulsion method were remained even after its polymerization, whereas about 25% of the epoxy groups originating from GMA were lost during the polymerization. When the storage temperature was kept at 50degreesC, almost all of the epoxy groups in both methods were lost quickly. Most of the epoxy groups in the miniemulsion method were gradually lost at 5degreesC by cross-linking with carboxyl groups during storage, whereas most of the epoxy groups obtained in the conventional method were gradually lost by hydrolysis. Their differences in reactivity or stability were considered to be due to the difference in hydrophilicity, molecular weight or polymerization method.