Recently, a study for eribulin mesylate(ERI), which is a useful drug for metastatic and recurrent breast cancer, reported that the absolute lymphocyte count(ALC)before administration is a useful prognostic factor. We retrospectively examined whether the results were reproducible in the patients with ERI. We examined the effect of ERI on the overall survival(OS)in 21 patients with HER2-negative metastatic and recurrent breast cancer who underwent treatment with ERI at our hospital. The clinical benefit ratio(CBR)was 57.1%. The median time to treatment failure(TTF)was 5.8 months and median OS was 19.9 months, showing a positive correlation between the TTF and OS. The factors that significantly prolonged the OS in univariate analysis were the TTF(<3 months vs ≥3 months, p<0.001), NLR(<3 vs ≥3, p=0.037), and ALC(<1,000/ μL vs ≥1,000/μL, p=0.008). In the multivariate analysis, TTF and ALC were the prognostic factors. The ERI outcome at our institution was good regardless of the subtype. The results of the multivariate analysis showed that TTF and ALC were factors that prolonged OS, and patients who received ERI for >3 months had good OS. Long-term administration of ERI was assumed to affect the immune microenvironment and prolong OS. Additionally, our data showed that the lymphocyte count before ERI administration is a simple and useful prognostic factor.