The aim of this open-label, multicenter, randomized phase II trial was to evaluate the efficacy and safety of zoledronic acid in combination with docetaxel in previously treated patients with non-small-cell lung cancer (NSCLC) and bone metastases. In this study, patients randomly received docetaxel (60 mg/m2) with (group DZ) or without (group D) zoledronic acid every 21 days. There were 50 patients in each group, and the primary endpoint was progression-free survival. In an efficacy analysis of 94 patients (DZ, 48; D, 46), the median progression-free survival was 2.7 months (95% confidence interval [CI], 1.5–3.5 months) for the DZ group and 2.6 months (95% CI, 1.5–3.4 months) for the D group (stratified log-rank test, P = 0.89). The median overall survival was 10.4 months (95% CI, 7.0–15.8 months) for the DZ group and 9.7 months (95% CI, 6.1–12.5 months) for the D group (stratified log-rank test, P = 0.62). There were no clinically relevant differences in the frequencies of grade 3 or 4 adverse events between the two groups. No treatment-related deaths occurred in the DZ group. Zoledronic acid combined with docetaxel was well tolerated but did not meet the primary endpoint of demonstrating a longer progression-free survival in advanced NSCLC patients with bone metastases compared with docetaxel alone. This trial was registered with the University Hospital Medical Information Network (UMIN000001098).