The present study was conducted to evaluate the toxic potential of tartrazine, a food color, in different tissues in adult rat: blood, liver, kidneys, and spleen. Tartrazine was administered orally at a dose of 300 mg/kg of body weight to adult male Wistar rats during a period of 30 days. Tartrazine treatment led to an increase in platelets count, a reduction in peripheral lymphocytes and in spleen T CD8-lymphocytes. Furthermore, tartrazine increased the activities of hepatocellular enzymes and promoted changes in kidney biomarkers. In order to explore the possible mechanism involved, oxidative-stress assessment was performed. Results identified critical oxidative alterations in all tested organs, as shown by the promotion of lipid peroxidation and the modification of endogenous antioxidant-defense enzymes. Thus, tartrazine is able to induce in adult rats’ hematotoxicity, immunotoxicity, and liver and kidney injuries by changing the whole balance between oxidants and antioxidants.