In this study, the effects of different cooking methods on health-promoting phytochemicals and antioxidant activity of fresh kale were investigated. Results showed that water soluble phytochemicals were significantly decreased by boiling. While stir-frying gave the highest degradation ratio for all phytochemicals, and steaming gave the lowest degradation ratio. The thermal degradation ratios of ascorbic acid, total carotenoids, total chlorophylls, total flavonols, and total phenolics content after stir-frying were 54.9, 28.2, 71.0, 81.3, and 39.3%, respectively. The results showed that steaming can be considered as the best method of cooking as it preserve the bioactive compounds and the antioxidant activity.