Topoisomerase IIα (TOPIIα) plays a key role in DNA replication and is a molecular target for TOPIIα inhibitor hemotherapy. A doxorubicin-based chemotherapy remains the most effective treatment for canine lymphoma, but there are no clear indications for its use in individual patients. The aim of this study was to assess the predictive value of TOPIIα expression in the treatment of canine lymphomas with TOPIIα inhibitors. Samples of formalin-fixed paraffin-embedded lymph nodes from 14 dogs with diffuse large B-cell lymphoma (DLBCL) and 5 dogs with peripheral T-cell lymphoma (PTCL) treated with a CHOP protocol were immunohistochemically labelled with anti-TOPIIα. Progression-free survival time (PFS) and overall survival time (OS) were estimated and compared with TOPIIα expression. Dogs with DLBCL had a higher level of TOPIIα expression compared to dogs with PTCL. The median PFS for dogs with DLBCL was significantly longer (260 days) than it was for dogs with PTCL (60 days). In DLBCL dogs with a high TOPIIα expression level, the median PFS was significantly longer (310 days) then it was in dogs with week or medium TOPIIα expression (51 days). The results of the study indicate that the immunohistochemical assessment of TOPIIα expression may be a valuable predictive indicator for anthracycline-based treatment of dogs with malignant lymphoma.