This study was designed to evaluate some immunological responses of male White Leghorn (WL) chicks kept on an ochratoxin A (OTA)-contaminated diet. For this purpose, 350 1-day-old male WL chicks were divided into five groups (A-E). Group A was kept as control, while Groups B, C, D, and E were fed OTA-contaminated feed at 0.1, 0.5, 1.0, and 1.5 mg/Kg diet, respectively, for 21 days, and then basal ration for the remaining period. At 14- and 16-days of age, random chicks (n = 10) from each group were used for analyses of phagocytic function of the reticuloendothelial system or for measuring the lymphoproliferative responses to intradermally-administered T-cell mitogen, phytohemagglutinin-P (PHA-P), respectively. At 30-days of age, abdominal macrophages were collected from 15 chicks/group and utilized for determination of their phagocytic potential and for nitrite production. Antibody (Ab) titers (i.e., total antibodies, IgM, and IgG) against sheep red blood cells (SRBC) were determined at 7 and 14 days after a primary (at 7 days of age) and a booster (given 14 days after primary [at 21-days of age]) dose (intravenous) of the antigen. Data from the present study showed that the relative weight of the bursa of Fabricius of chicks fed OTA for 14 and 21 days and the spleen of chicks fed OTA for 21 days were significantly lower than their control counterpart. Phagocytic function of reticuloendothelial system evaluated by carbon clearance, and lymphoproliferative response to PHA-P, of chicks kept on OTA-contaminated diet were significantly lowered. The percentage of abdominal macrophages displaying phagocytosis of SRBC, the number of SRBC/macrophage, and nitrite production were each significantly lower in cells from chicks in the OTA-fed groups. Total Ab (at days 7 and 14 post-booster SRBC injection) and IgG (at day 14 post-primary and day 7 post-booster SRBC injection) titers against SRBC showed significant reductions in the groups fed OTA-contaminated diet. The findings of this study are in line with the previous work suggesting the immunosuppressive effect of OTA in male WL chicks regarding functional impairment in some of the components of the immune system.