Ochratoxin A (OTA) is a fungal mycotoxin that affects animal and human health. Rabbits are very sensitive to OTA, but there is limited data about its deleterious effects on these animals. This study aimed to evaluate pathological changes and potential immunosuppression in young New Zealand White rabbits exposed to 2 ppm OTA via dietary administration for 30 days. All rabbits were immunized against RHDV, and blood samples were collected for serological examination before immunization and on day 28 afterward. The blood for clinical biochemistry and samples from internal organs for pathomorphological investigations were taken at the end of the experiment. A potent immunosuppressive effect of OTA on the humoral immune response against RHDV was observed, evidenced by a decrease in antibody titers (p<0.005). The immunosuppressive effect of OTA caused the occurrence of a secondary infection (pasteurellosis), which resulted in the death of two rabbits from the OTA-exposed group. Biochemical investigations revealed decreased levels of glucose and increased levels of creatinine, BUN, triglycerides, ALT, AST, and ALP. Pathomorphological investigations revealed the that strongest damage occurred in the liver, kidneys, spleen, and thymus, except in cases of secondary pasteurellosis, where the strongest damage was found in the lung. In the kidneys, the main degenerative changes were found in the epithelium of proximal tubules. Liver damage included degeneration in hepatocytes and Kupffer cell activation. In the spleen and thymus, degenerative lesions and/or cell depletion were seen. Lung damage, especially in cases of secondary Pasteurellosis, included purulent or croupous pneumonia, fibrinous pleurisy, and thrombosis of vessels. In conclusion, it was found that immunosuppression was the first pronounced toxic effect of OTA and that it may manifest clinically before pathological and biochemical changes. Humoral immunity was affected to the extent of allowing the development of clinical disease and death of rabbits at only 2 ppm OTA in the ration.