Objective: The Dengzhan Shengmai (DZSM) capsule is a commercially available type of Chinese herbal medicine frequently administered to improve neurological impairment after stroke. Its ability to prevent recurrent stroke, however, has not been determined. This study therefore evaluated the ability of DZSM as an add-on to conventional secondary preventive agents to prevent recurrent ischemic stroke. Methods: In this randomised, double-blind, placebo-controlled trial, conducted at 83 hospitals in Mainland China, 3143 patients in 14-180 days after the initial onset of ischemic stroke, were randomly allocated to the DZSM (0.36 g, twice daily for 12 months) or the placebo group. All patients in both groups received standard secondary preventive medications. The primary outcome was the 1-year incidence of stroke. Between group differences were assessed using the Cox proportional hazards model. Results: Intent-to-treat analysis showed that 58 (3.8%) participants in the DZSM group and 82 (5.4%) in the placebo group experienced new stroke events (hazard ratio = 0.70, 95% confidence interval = 0.50-0.98, P = 0.036). The type and incidence of adverse events were similar in the DZSM and placebo groups. Conclusions: The addition of DZSM capsules to standard secondary preventive agents provides additional benefits after the initial onset of ischemic stroke, reducing recurrent stroke without increasing severe adverse events. However, further study is needed to elucidate the role of DZSM on the updated practice of conventional secondary prevention for ischemic stroke.