Objective: To study the changes of adenosine diphosphate (ADP)-induced platelet aggregation rate, and evaluate the effects of Maixuekang Capsule (MKC) on platelet aggregation rate and long-term prognosis of patients with acute coronary syndrome after percutaneous coronary intervention (PCI). Methods: A total of 236 patients with acute coronary syndrome, who received successful PCI, were randomly assigned to a trial group (116 cases) and a control group (120 cases) according to random numbers; treatment allocation occurred when the participants met the inclusion criteria and signed the informed consent forms. In the trial group, the patients were treated with MKC combined with routine medication, and in the control group the patients were treated with routine medication. The therapeutic course for the two groups was 12 months and the follow-up was 12 months. The levels of ADP-induced platelet aggregation rate and serum high-sensitive C-reactive protein (hs-CRP) were determined before PCI, 12 h and 30 days after PCI. In the meantime, the incidence of cardio-/cerebrovascular events was recorded during the 12-month follow-up. Results: Compared with before PCI, the levels of ADP-induced platelet aggregation rate and serum hs-CRP were significantly higher at 12 h after PCI (P<0.05). They were significantly reduced after 30-day-treatment of MKC, showing statistical differences when compared with those in the control group (P<0.05). During the 12-month follow-up, the incidence of cardio-/cerebrovascular events was significantly lower in the trial group than in the control group (6.9% vs. 12.5%, P<0.01). Conclusions: ADP-induced platelet aggregation function was significantly elevated after PCI. MKC improved the prognosis of patients with acute coronary syndrome, possibly through inhibiting the platelet aggregation, fighting against inflammation, and protecting the vascular endothelial function.