In this study, the effect of heparin-derived oligosaccharide (HDO) on bovine vascular smooth muscle cell (VSMC) proliferation and signal transduction mechanism involved were investigated.  The levels of PKC-α protein and mRNA were determined by cell-based ELISA, RT-PCR, Western blotting and immunocytochemical methods.  Meanwhile, mRNA levels of c-jun, c-myc and c-fos were assayed by RT-PCR method.  The results showed that HDO inhibited newborn calf serum (NCS)-induced expression of PKC-α and proto-oncogenes, which may be one of the mechanisms for the inhibition of VSMC proliferation by HDO.  Flow cytometry analysis indicated that HDO blocked NCS-induced cell cycle progression by arresting cells at G₀/G₁ phase.  The results imply that HDO inhibits VSMC proliferation by moderating the gene level of PKC-α, eventually inhibiting proto-oncogene mRNA expression and blocking G₁/S transition.