Background: Toxoplasmosis is a global zoonotic disease, that is mainly asymptomatic in healthy persons, but critical and life-threatening in immunocompromised patients. The infection is caused by an opportunistic obligate intracellular parasite protozoon “Toxoplasma gondii” (T. gondii) that can cause fatal complications in immunosuppressed patients. Cancer patients are being immunocompromised from the cancer itself and on the other hand cancer therapy they receive may reactive a latent T. gondii infection that leaves them at high risk. The B-cell activating Factor (BAFF) is a cytokine that plays an essential role in the activation, maturation, and survival of B cells. It is vital for the appropriate functioning of the immune system. Monitoring BAFF levels in cancer patients undergoing chemotherapy could be important for preventing or controlling infections in these vulnerable patients. Objectives: This study aimed to detect seroprevalence of T. gondii in cancer patients receiving chemotherapy and assess the levels of BAFF in those patients. Materials and Methods: 150 serum samples were collected from oncology patients having different types of cancer and receiving chemotherapy, from different ages. And 30 samples from healthy people for control. In this cross-sectional study, samples were collected from the 1st of October 2023 to the 1st of March 2024, at Kirkuk Oncology and Hematology center. The method used was the Sandwich Enzyme-Linked Immunosorbent Assay (Sandwich-ELISA) technique. Results: the overall anti-T. gondii IgG and IgM seropositive samples were found to be 67 (37.2%) in the total study population and 67(44.7%) in cancer patients. BAFF levels were elevated in cancer patients infected with T. gondii compared with the cancer patients with no infection and the healthy control group. A significant difference was indicated with (p-value 0.0004). Conclusions: A high rate of T. gondii seroprevalence was revealed among oncology patients receiving chemotherapy with elevated levels of BAFF associated with T. gondii infection in those patients.