Introduction: Bendamustine has been reported to be effective against low-grade B-cell lymphoma. We examined the effect of bendamustine on the lymphocyte-monocyte ratio (LMR) in low-grade B-cell lymphoma patients., Methods: We retrospectively reviewed 127 cases of first line or relapse/refractory low-grade B-cell lymphoma in three individual institutions (Asahikawa Municipal Hospital, Aiiku Hospital, and Hakodate Municipal Hospital). Only patients who had received at least three courses of bendamustine therapy were selected; the LMR was evaluated at starting the initial course of bendamustine therapy. Time to next treatment (TTNT) was used to ascertain the efficacy of bendamustine therapy., Results: Follicular lymphoma (FL), at 68.5% (87/127), is the most common histological subtype of low-grade B-cell lymphoma. The receiver operating characteristic (ROC) curve for the LMR showed a cutoff value of 2.0, and 33 cases (26.0%) had an LMR ≤2.0. Cases with LMR ≤2.0 had a significantly earlier progression than those with LMR > 2.0, based on the TTNT (P = .0007). Additionally, LMR ≤2.0 indicates earlier progression in TTNT when comparing only FL and low-grade B-cell lymphoma cases without FL (P = .007, 0.002). For multivariate analysis, the factors associated with an LMR ≤2.0 (HR, 2.741; 95% CI, 1.4330-5.245; P = .002) were considered as early progression factors with regard to the TTNT., Conclusion: Lymphocyte-monocyte ratio effectively predicts the efficacy of bendamustine therapy for low-grade B-cell lymphoma, particularly FL; its application may improve treatment strategies for this disease., (© 2020 John Wiley & Sons Ltd.)