Thrombin acts as a potent mitogenic factor for ECs (endothelial cells) by the release of several growth factors, including PDGF-B (platelet-derived growth factor-B). CBP (CREB-binding protein), which functions as a transcriptional coactivator, links the changes in the extracellular stimuli with alterations in gene expression. Therefore, we hypothesized that CBP could mediate thrombin-induced proliferation of ECs via PDGF-B-dependent way. Short hairpin RNA was used to down-regulate the expression of CBP in ECs. CBP and PDGF-B levels were analysed by real-time RT-PCR and Western blot. To evaluate ECs proliferation, cell cycle and DNA synthesis were analysed by flow cytometry and BrdU (bromodeoxyuridine) incorporation assay, respectively. PDGF-B was involved in the mitogenic effect of thrombin on ECs. Down-regulation of CBP attenuated ECs proliferation and inhibited cell cycle progression induced by thrombin. Silencing CBP expression also suppressed thrombin-induced PDGF-B expression in ECs. Mitogenic activity of thrombin was impaired by silencing CBP expression in ECs. This inhibitory effect was, in part, related to the inability to up-regulate PDGF-B expression in ECs. CBP could be regarded as a potential therapeutic target for vascular injury.