Background To report our findings on quality of life (QoL) in a randomized phase II study to determine the optimal dose of 3-week cycle nab-paclitaxel (q3w nab-PTX) in patients with metastatic breast cancer (MBC). Methods Patients with HER2-negative MBC were randomly assigned to three different doses of q3w nab-PTX (SD 260 mg/m 2 vs. MD: 220 mg/m 2 vs. LD 180 mg/m 2 ). QoL was assessed at baseline and during the second, fourth and sixth courses of treatment using the Functional Assessment of Cancer Therapy-Taxane (FACT-Taxane), Cancer Fatigue Scale (CFS) and EuroQol 5-Dimension (EQ-5D). Comparisons were performed with mixed-model repeated measures (MMRM). Results A total of 141 patients were enrolled in the parent study, and 136 (96%) (44, 45 and 47 in the SD, MD, and LD groups) were included in the analysis. MMRM analysis showed that the difference from the baseline FACT-Taxane trial outcome index at MD and LD were significantly higher than that at SD (MD vs. SD P  < 0.001, LD vs. SD P  < 0.001). Differences from baseline for FACT-Taxane total, physical and emotional well-being, and taxane subscale scores at MD and LD were also higher than at SD. The difference from baseline for the CFS score at LD was lower than at SD ( P  = 0.013) and those for EQ-5D utility scores at MD and LD were higher than at SD (MD vs. SD P  = 0.011, LD vs. SD P  < 0.001). Conclusion QoL of patients treated with 220 or 180 mg/m 2 of q3w nab-PTX was significantly better than that of patients treated with 260 mg/m 2 . Trial registration The protocol was registered at the website of the University Hospital Medical Information Network (UMIN), Japan (protocol ID: UMIN000015516), on 01/11/2014. Details are available at the following address: https://upload.umin.ac.jp/cgi-open-bin/ctr_e/ctr_view.cgi?recptno=R000017916