Constituents of garlic oil are reported to possess immunomodulatory, antioxidant, and anticancer effects. Use of tartrazine as a food colouring-compound is associated with significant toxicity on the body. The present study was conducted to evaluate the protective effect of garlic oil on haemato-immunotoxicity induced by tartrazine. Male Wistar albino rats were treated orally with 40 mg garlic oil/kg body weight thirty minutes before the administration of 300 mg tartrazine/kg body weight for thirty consecutive days. Twenty-four hours after the last garlic oil and tartrazine dose, blood and spleen were harvested to analyse toxicity-related parameters. The tartrazine treatment induced significant changes in the body weight gain, relative spleen weight, haematological parameters, proliferation rate of splenocytes, and percentage of T-cell subtypes in the spleen, as detected by flow cytometric analysis, in male rats. Moreover, oxidative stress in the spleen tissue and hepatic and renal dysfunction were detected after exposure to tartrazine. Treatment with garlic oil showed significant reduction in overall toxicity in the tartrazine-treated rats. The antitoxic effects of garlic oil were associated with the induction of antioxidant mechanisms. In conclusion, garlic oil can lower tartrazine-induced haemato-immunotoxicity through its antioxidant activity.