The aim of this study was to evaluate the efficacy and safety of the combination of docetaxel (TXT) plus tamoxifen (TAM) in advanced non-small-cell lung cancer (NSCLC) patients who had received platinum-based first-line chemotherapy. A total of 120 advanced NSCLC patients pretreated with platinum-based chemotherapy were randomized into two treatment groups (the TXT and TXT+TAM groups) in a 1 : 1 ratio. Reversal of P-glycoprotein (P-gp) expression, tumor response, progression-free survival, overall survival, and safety were evaluated on an intention-to-treat basis. The median number of cycles of allocated chemotherapy was four in each treatment group (range: 2–6 cycles). The overall response rate and disease control rate in the TXT+TAM group were significantly higher than those in the TXT group (36.7 vs. 15.0% for overall response rate, P=0.007; 85.0 vs. 68.3% for disease control rate, P=0.031). The combination of TXT and TAM could effectively reverse P-gp expression in tumor tissues and provide a significant survival benefit for advanced NSCLC patients compared with TXT alone (11.6 vs. 9.1 months, P=0.030). In addition, in the TXT+TAM group, patients achieving P-gp reversal had a significantly greater median progression-free survival and overall survival than nonreversal patients. Furthermore, the combined therapy showed a safety profile comparable to that of TXT. The combination of TXT and TAM may be an effective and safe treatment option for advanced NSCLC patients who have already developed P-gp-mediated multidrug resistance.