PELI is a family of E3 ubiquitin ligases that regulate protein activity through a post-translational modification, ubiquitination. While PELI1 has been found to play a pivotal role in inflammatory processes through the activation of Toll-like receptor signaling and the NF-kB pathway, the role of PELI1 in oncogenesis has not been the subject of much investigation. We aimed to explore PELI1 expression in various malignant lymphomas and identify clinicopathologic significance. Immunohistochemistry for PELI1 was performed on a total of 502 cases, including 406 B-cell, 76 T or NK-cell, and 20 Hodgkin lymphomas. High expression of PELI1 was found in high-grade B-cell lymphoma cases such as diffuse large B-cell lymphoma, Burkitt lymphoma, and plasmablastic lymphoma, whereas low-grade B-cell lymphoma, T/NK-cell lymphoma, and Hodgkin lymphoma cases showed very low levels of expression. In vitro cell line studies, the results of western blot, and RT-PCR were concordant with those of the immunohistochemical results; RL7, Pfeiffer, SUDHL-2, DOHH2, and Ramos cell lines showed high levels of PELI1 protein and mRNA expression. In 182 diffuse large B-cell lymphoma, PELI1 expression was positively correlated with the expression of MYC, BCL6, BCL2, and MUM1 (Spearman's ρ=0.427, 0.507, 0.246, and 0.137, respectively; P<0.001, <0.001, 0.001, and 0.066, respectively). In diffuse large B-cell lymphoma, high expression of PELI1 was associated with frequent bone marrow involvement (P=0.013) and shorter relapse-free survival (P=0.002). Our results suggest that PELI1 might participate in B-cell maturation or oncogenic activation of aggressive B-cell lymphomas, both during and after germinal center stages.