By using sodium dodecyl sulfate (SDS) as an emulsifier, polymerization of N-butyl maleimide (NBMI) was carried out in ternary oil-in-water microemulsion, initiated with potassium persulfate (KPS). The kinetics of microemulsion polymerization were measured by dilatometry. The effects of initiator concentration, polymerization temperature, monomer concentration, and emulsifier concentration on polymerization kinetics were investigated. On this basis, the polymerization kinetics were discussed. The experiment result showed that the microemulsion polymerization kinetics of N-butyl maleimide were almost consistent with the prediction of the Smith-Ewart theory in conventional emulsion polymerization, except that the emulsifier showed a special effect on polymerization. At the same time, the polymer was characterized by IR, H-1-NMR, DSC, and TGA.