Background: The Advanced Lung Cancer Inflammation Index (ALI, body mass index × albumin/neutrophil-to-lymphocyte ratio) has been demonstrated to be a prognostic factor of survival in some solid cancers. We retrospectively investigated the usefulness of the ALI to predict chemotherapy response and survival in 212 patients with diffuse large B cell lymphoma (DLBCL) treated with R-CHOP (rituximab, cyclophosphamide, doxorubicin, vincristine, and prednisolone) chemotherapy. Methods: Patients were allocated to a low ALI group (n = 82, 38.7%) or a high ALI group (n = 130, 61.3%) according to an optimal pretreatment ALI cut-off value of 15.5 as determined by receiver operating curve analysis. Results: The low ALI group displayed more adverse clinical characteristics, lower rates of complete remission (54.9 vs. 75.4%, p = 0.008), and poorer 5-year progression-free (PFS, 58.1 vs. 77.3%, p = 0.006) and overall (OS, 64.2 vs. 80.2%, p = 0.008) survival. Multivariate analysis showed that low ALI was found to independently predict shorter PFS and OS. Interestingly, a low ALI reverted to a high ALI during treatment in 58 patients (27.4%), and the 5-year OS of these patients was better than that of patients whose ALI remained low (n = 24, 72.5 vs. 24%, p < 0.001). Conclusions: ALI might be an easily available marker for predicting clinical outcomes in DLBCL patients treated with R-CHOP chemotherapy.