Radiation polymerization of butyl acrylate was carried out in a microemulsion stabilized with sodium 12-butinoyloxy-9-octadecenate (SBOA). The stable and reddish latex with high poly mer content and low emulsifier content was successfully produced in this way. It was found that, for most cases, the polymerization rate shows three intervals : the increasing period, the plateau period, and the decreasing period. The length of the nucleation period becomes longer at a higher dose rate (D) and lower emulsifier content (E). The plateau region of polymerization rate is lengthened with the increase of monomer and emulsifier content and shortened with the increase of dose rate. It was shown that monomer content, emulsifier content, and dose rate have great effects on R(p) (the polymerization rate in the plateau region, or the maximum polymerization rate during polymerization) and M(n) (the molecular weight of the polymer). R(p) proportional to[M]D-0.93(1.27)[E](-1.07;) M(n) proportional to [M]D-0.65(0.28)[E](-1.66). The polymerization mechanism is discussed based on these results.