A series of polymerized high internal phase emulsion (polyHIPE) monoliths with internal phase contents varying from 82.5 to 94.0 % were synthesized. The limited spaces of the polyHIPE were used as reactors to polymerize methyl methacrylate (MMA) by reverse atom transfer radical polymerization (RATRP). The main purpose of this research was to investigate the effect of limited spaces of polyHIPE on RATRP polymerization. The monoliths before and after MMA polymerization and PMMA obtained in the polyHIPE were characterized by scanning electron microscopy, gel permeation chromatography, Fourier transform infrared spectroscopy, thermogravimetry analysis, hydrogen nuclear magnetic resonance, and differential scanning calorimetry. The results suggested that the monomer MMA had polymerized in the polyHIPE. Compared with PMMA by RATRP without confined space, the molecular weight, initial thermal decomposition temperature, glass transition temperature (T (g)), and the isotacticity of the PMMA obtained from polyHIPE were increased significantly and the molecular weight distribution broadened. The increase in the internal phase contents increased the numbers of the cavities and windows, whereas the molecular weight, molecular weight distribution, and T (g) of the PMMA obtained from different polyHIPEs did not change much.