To study the changes of adenosine diphosphate (ADP)-induced platelet aggregation rate, and evaluate the effects of Maixuekang Capsule (MC) on the platelet aggregation rate, high-sensitive C-reactive protein (hs-CRP) and the long-term prognosis in patients with acute coronary syndrome under percutaneous coronary intervention (PCI). Totally 236 inpatients with acute coronary syndrome under PCI, who successively received PCI from July 2008 to June 2010, were randomly assigned to the routine treatment group (RTT, 120 cases) and the MC treatment group (MKT, 116 cases). Besides routine medication, patients in the MKT group additionally took MC, 12 capsules daily for 12 successive months. The ADP-induced platelet aggregation rate and hs-CRP concentration were determined before PCI, 12 h and 30 days after PCI. In the meantime, the incidence of adverse cardio-/cerebrovascular events was recorded during the twelve-month clinical follow-up. Results Compared with before PCI, ADP-induced platelet aggregation rate and the serum hs-CRP concentration were significantly higher 12 h after PCI (P < 0.05). They were significantly reduced after 30-day treatment of MC, showing statistical difference when compared with those in the RTT group (P < 0.05). In the 12-month follow-up, the incidence of adverse cardio-/cerebrovascular events was significantly lower in the MKT group than in the RTT group (6.9% vs 12.5%, P < 0.01). ADP-induced platelet aggregation function was significantly elevated after PCI, which was a predictive factor of poor coronary events. MC improved the long-term prognosis of patients with acute coronary syndrome possibly through inhibiting the platelet aggregation rate and the hs-CRP concentration.