The purpose of this study was to analyze the pre- and post-treatment neutrophil to lymphocyte ratio (pre- and post-NLR) in combination with immunologic profiles in patients with diffuse large B-cell lymphoma (DLBCL) treated with rituximab, cyclophosphamide, doxorubicin, vincristine and prednisone (R-CHOP). A total of 447 newly diagnosed patients with DLBCL treated with R-CHOP were analyzed retrospectively. A pre-NLR ≥ 3 was independently associated with poor progression-free survival (PFS) (hazard ratio [HR] = 2.19, p < 0.001) and overall survival (OS) (HR = 2.89, p < 0.001). In patients with high pre-NLR, reduction of the post-NLR to < 3 after R-CHOP was correlated with improved survival. Low pre-NLR (< 3) was also associated with a higher number of peripheral CD19 + lymphocytes (p = 0.049) and NK cells (p = 0.031). In conclusion, a pre-NLR ≥ 3 was an independent prognostic factor for PFS and OS in patients with DLBCL treated with R-CHOP.