The aim of this study was to determine the oxidative stress and changes of some biochemical parameters in calves with leptspirosis. In this study, 20 calves were used consisting of 10 healthy calves and 10 calves with leptospirosis. The malondialdehide (MDA), plasma catalase (CAT), glutathiyon peroxidase (GSH-Px), total protein, albumin, alkaline phosphatase (ALP), aspartat amino transferase (AST), lactate dehydrogenase (LDH), gama glutamyl transferase (GGT), blood urea nitrogen (BUN), glucose and total bilirubin levels were determined in all calves. The MDA levels was higher in the infected calves compared to control, but GSH-Px ve CAT levels were lower. ALP, AST, LDH, GGT, BUN, total bilirubin and total protein levels was higher in sick calves compared to controls, but albumine and ve glucose levels was lower in the infected calves. In conclusion, the oxidative stress was determined during leptospirosis. Furthermore, the biohemical changes to evidence that liver andrenal injury was determined during leptospirosis.