Inverse emulsion copolymerization of acrylamide (AM) and acrylonitrile (AN) was studied with a semi-batch process. ,Molecular weight of copolymers prepared under was measured Correlating molecular weight obtained by lightscattering method with intrinsic viscosity of copolymer solution in DMF, a Mark-Houwink relationship was derived. Effects of reaction temperature and concentrations of initiator, reducing agent and emulsifier on molecular weight were also studied. Results exhibited a large deviation from Smith-Ewart''s ideal emulsion polymerization mechanism, probably due to coexistence of emulsion and solution polymerization caused by different solubilities of AM and AN in water and solvent. The relatively broad particle size distribution indirectly supports the coexistence of two polymerization schemes.