Aim: To evaluate the safety and efficacy of an extract of Ganoderma lucidum that shows the strongest 5α-reductase inhibitory activity among the extracts of 19 edible and medicinal mushrooms by a double-blind, placebo-controlled, randomized and dose-ranging study in men with lower urinary tract symptoms (LUTS). Methods: In this trial, we randomly assigned 88 men over the age of 49 years who had slight-to-moderate LUTS to 12 weeks of treatment with G. Lucidum extract (6 mg once a day) or placebo. The primary outcome measures were changes in the International Prostate Symptom Score (IPSS) and variables of uroflowmetry. Secondary outcome measures included changes in prostate size, residual urinary volume after voiding, laboratory values and the reported adverse effects. Results: G. Lucidum was effective and significantly superior to placebo for improving total IPSS with 2.1 points decreasing at the end of treatment (mean difference, -1.18 points; 95% confidence interval, -1.74 to -0.62; P < 0.0001). No changes were observed with respect to quality of life scores, peak urinary flow, mean urinary flow, residual urine, prostate volume, serum prostate-specific antigen or testosterone levels. Overall treatment was well tolerated with no severe adverse effects. Conclusion: The extract of G. Lucidum was well tolerated and improved IPSS scores. These results encouraged a further, large-scale evaluation of phytotherapy for a long duration using the extract of G. Lucidum on men with LUTS.