Ethnopharmacological relevance: Wuling Capsule is a single herbal formula from mycelia of precious Xylaria nigripes (KI.) Sacc and its pharmacological function have a tranquilizing effect on the central nervous system. The aim of the study to evaluate the efficacy and safety of Wuling capsule in treatment of insomnia. Materials and methods: We performed a multicenter, randomized, double-blind, placebo-controlled study. The participants received either placebo (n=92) or Wuling capsule (n=94) for 4 weeks and a follow-up period for 2 weeks. Results: Compared between pre-treatment and post-treatment, the global Pittsburgh sleep quality index (PSQI) scores in both Wuling capsule group and placebo group improved significantly (P<0.01). However, there was no significant difference between Wuling capsule group and placebo group (P>0.05). Scores of clinical global impressions scale (CGI-I) at each week in Wuling capsule group was similar to those in placebo group (P>0.05). Compared between pre-treatment and post-treatment, scores of the four components of world health organization on quality of life brief scale (WHOQOL-BREF) in both Wuling capsule group and placebo group improved significantly (P<0.01). However, there were no difference between the two groups (P>0.05). The rate of adverse events was 10.10% in Wuling group, and 6.73% in placebo group (P>0.05). Conclusions: Wuling capsule can improve insomnia when compared with pre-treatment for 4 weeks and be a well tolerated by all the patients at the 6 weeks of study period. However, there are no significant in the results of the variables tested when compared with placebo control. Further additional rigorous randomized clinical trials are still required. (C) 2012 Elsevier Ireland Ltd. All rights reserved.