Aim The effects of heparin and low molecular weight heparin (LMWH) on the growth of cultured human aortic smooth muscle cells(hASMCs) was studied in this article. Methods The thirth-passage hASMCs were planted onto 24-well plate. After incubated for 24 h in media supplemented with 10%human serum(HS) and 10%fetal calf serum(FCS), media were changed into low concentration serum(0.5% HS, 0.5%FCS)and continued to incubate for 24 h and cultured by DMEM containing 10%HS either old or fresh, 10%FCS and different concentration of heparin or LMWH (heparin and LMWH were presented as hexuronic acid) together with corresponding control groups (without heparin or LMWH) for 24 h, hASMCs growth was estimated both morphologically and by 3 H-TdR incorporation. Results Both heparin and LMWH inhibited the proliferation of well-growth hASMCs, the inhibition rates were 66%, 69%, 69%, and 60%, 68%, 67%, respectively, with no concentration dependent relationship. hASMCs of control (with old HS stored at 4℃ for 2 years) shrank and showed poor-growth pattern while those in groups of different concentrations of LMWH or heparin became well-spread and well-growth pattern. Both heparin and LMWH promoted the proliferation of poor-growth hASMCs, the stimulation rates were 149%, 140%, 180%, and 207%, 246%, 309%, respectively. Conclusions Heparin and LMWH have a dual regulative role (inhibition and promotion) in hASMCs growth. It indicate that they may play an important role in controlling the proliferation of vascular smooth muscle cells and maintaining the integrity of vascular structure.