Cadmium is an element used widely in modern industry and which is quite toxic for living beings. Cadmium, usually the result of the anthropogenic activities such as industry and agriculture, reaches water systems and aquatic living beings are exposed to that pollutant at a high level. In order to understand better the effect of cadmium on aquatic organisms, it is quite important to identify the chemical and physiological processes involved in the intake, the accumulation, the conservation, and the release of cadmium. Thus, enzymatic activities are frequently used to study the effect of toxic substances on living beings. In this study, the research made on the effect of cadmium on the enzyme activities of Superoxide dismutase (SOD), Catalase (CAT), Glutathione peroxidase (GSH-Px), Glucose-6-phosphate dehydrogenase (G6PD), Aspartate aminotransferase (AST), Alanine aminotransferase (ALT), Alkaline phosphatase (ALP) and Lactate dehydrogenase (LDH) and on the malondialdehyde (MDA) levels in different tissues of some freshwater fishes were studied.