Gosha-jinki-gan (GJG), a traditional Chinese medicine, is known to be potentially effective for urinary disturbance. For the clinical evaluation of Gosha-jinki-gan, we administered GJG for 6 weeks to elderly male patients with overactive bladder (OAB) and assessed its efficacy and tolerability. In this study, 30 male patients with over 6 months of OAB symptoms had received 2.5 g GJG mixture x 3/day. After 6 weeks of treatment, the efficacy, safety, and tolerability were assessed. We evaluated International Prostate Symptom Score (I-PSS), Overactive Bladder Symptom Score (OABSS), quality of life (QOL), maximal urinary flow rate (Qmax), average urinary flow rate (Qave), incidence of urinary incontinence, and post-void residual before and after treatment. We observed significant improvements in I-PSS (15.2 +/- 1.0 vs. 12.0 +/- 0.9, p < 0.0001), OABSS (7.5 +/- 0.6 vs. 4.9 +/- 0.5, p < 0.0001), and QOL score (4.4 +/- 1.0 vs. 3.3 +/- 1.1, p < 0.0001, Wilcoxon rank sum test). GJG was significantly effective in improving urgency, micturition frequency, nocturia, and urinary incontinence (p < 0.05). However, Qmax, Qave, and post void residual did not significantly change. Mild adverse effects were observed in 3 cases. The symptoms were diarrhea, nausea, and urinary frequency. These data suggest that Gosha-jinki-gan may be a new potential therapeutic agent for OAB without deterioration of voiding function in men with benign prostatic obstruction (BPO).