Abstract: In this study, the effect of heparin-derived oligosaccharide (HDO) on platelet-derived growth factor (PDGF) induced vascular smooth muscle cells (VSMCs) proliferation and the related signal transduction mechanisms were investigated. MTT assays were used to measure VSMCs proliferation. Cell cycle distribution was analyzed by flow cytometry. The level of key regulatory proteins in PKC, MAPK and Akt/PI3K pathways were determined by RT-PCR, Western blot and immunocytochemical methods. Meanwhile, mRNA expressions of some proto-oncogenes were assayed by RT-PCR method. Our data showed that HDO (0.01, 0.1 and 1 �mol·L^-1) inhibited 30 ng·mL^-1 PDGF-induced VSMCs proliferation in a dose-dependent manner, blocked the G₁/S transition and inhibited the level of key regulatory proteins and some proto-oncogenes (P < 0.05). The results showed that HDO may decrease the key regulatory proteins expression, hence suppress the transcription of proto-oncogene and G₁/S transition, finally inhibiting VSMCs proliferation.