Objective:To observe the efficacy and safety of Yangxue Ruanjian capsule in the treatment of knee osteoarthritis. MethodsIn this randomized, double-blind, placebo-controlled study, 84 patients with knee osteoarthritis were randomly assigned into control group and treatment group, 42 patients in each group. The treatment group was given Yangxue Ruanjian capsule and the control group received placebo. The treatment course was 4 weeks in both groups. The changes in TCM syndrome score and the total score, pain sub-score, stiffness sub-score and joint function sub-score of Western Ontario and McMaster Osteoarthritis Index (WOMAC) were observed and safety was evaluated before treatment and at 2 and 4 weeks of treatment.  Results:①All of the 84 patients completed the visit at 2 weeks of treatment; at 4 weeks of treatment, there were 6 and 7 dropouts (lost to follow-up) in the treatment group and the control groups, respectively. ②There were no significant differences in WOMAC total score or sub-scores in the groups before treatment and at 2 weeks of treatment (P＞0.05). At 4 weeks of treatment, WOMAC total score and sub-scores decreased compared to those before treatment in the treatment group (P＜0.05), and WOMAC total score, pain sub-score and joint function sub-score decreased in the control group (P＜0.05).③There were greater differences in WOMAC total scores and sub-scores in the treatment group than in the control group at 2 vs. 4 weeks of treatment and before treatment vs. at 4 weeks of treatment (P＜0.05). ④The TCM syndrome score decreased in both groups before treatment vs. at 2 and 4 weeks of treatment (P＜0.05). There were no significant differences in TCM syndrome score at any time point between the groups (P＞0.05).  Conclusion:Yangxue Ruanjian capsule effectively relieves the symptoms of patients with knee osteoarthritis with good safety, including joint pain, stiffness and dysfunction, showing the value for further research and development.