The object of the research was to determine the antioxidant effect of cassia essential oil on deep-fried beef during the frying process. The rules and optimum processing conditions of deep-fried beef with addition of cassia essential oil were discussed through an orthogonal experiment and some single factor experiments (frying time, frying temperature, oil types and concentration of essential oil). The antioxidant effect was evaluated by peroxide and TBA value. Results showed that the antioxidant effect of cassia oil during the frying process was optimum under the conditions of 30 μL cassia oil/250 mL palm oil, 1.5 min at 150 °C. The main compositions of cassia oil were analysed by GC–MS method.