Sodium sulfohexyl methacrylate (SSHMA) was copolymerized with methyl methacry-late (MMA)，hydroxyethyl methacrylate (HEMA) and n-hexyl methacrylate (HMA)．The reactivity ratios of various monomers with SSHMA(M1) were：for MMA，r1=1.12±0.01，r2=0.77±0.01；forHEMA，r1=0.86±0.02，r2=0.93±0.05；forHMA，r1=0.57±0.03， r2=0.59±0.23 (in DMSo)；and for HEMA，r1=0.49±0.01，r2=1.01±0.04 (in wa-ter)．The average values of the copolymerization parameters calculated from the monomer reactivity ratios were Q=1.015 and e=+0.844．The polymerization reaction order of SSHMA with respect to initiator was 0.51 and that with respect to monomer was 1.91 in water soludon，and was 0.53 and 1.91 respectively in DMSO，but the ratio of the rate con-stant KpKt1-2 in water was greater．Tests of heparin-retarded blood coagulation time sho-wed that the anticoagulant activity of poly SSHMA is independent of molecular weight wi-thin the range from 1.3×105 to 10.4×105．