The objective of this study was to evaluate the efficacy and toxicity of capecitabine in metastatic breast cancer (mBC) according to the estimated glomerular filtration rate (eGFR). A total of 135 patients included in the final analysis were stratified into 3 categories according to baseline eGFR, i.e., eGFR <60 mL/min/1.73 m(2) (Group 1), eGFR 60-90 mL/min/1.73 m(2) (Group 2) and eGFR >90 mL/min/1.73 m(2) (Group 3). If a patient developed a level of toxicity that would lead to capecitabine dose reduction, this was recognized as dose-limiting toxicity (DLT). The dose was reduced due to toxicity in 95 cycles. A total of 95 DLTs were seen in 76 (56.2%) of the 135 patients. When 76 patients with DLT were evaluated according to eGFR, DLT was observed in 93.3% of those in Group 1, 72.5% of those in Group 2 and 41.3% of those in Group 3 (p < 0.001). The median time to progression (TTP) of all patients was 7.4 months. No significant difference in TTP was observed in patients stratified into 3 groups according to eGFR. When the patients were divided into two groups as DLT and without DLT, the median TTP was 8.68 months (95% CI, 7.53-9.81 months) in those with toxicity and 6.23 months (95% CI, 4.04-8.43 months) in those without toxicity (log-rank p = 0.004). We found a significant relationship between low eGFR and increased risk of DLT. Having a DLT was associated with a longer TTP. It indicates the need for more data/larger study investigating these discrepancies.