Dietary vegetables contain a wide variety of free radical-scavenging antioxidants such as phenolic compounds and anti-oxidative vitamins. Epidemiological studies have been shown that vegetable consumption is associated with a reduced risk of life-style related diseases such as cancer and coronary heart diseases. Therefore, antioxidants in vegetables have been received considerable attention in recent years for their role in human health. In Japan, the recommended intake of vegetables is 350 g/day.   Vegetables are usually consumed after thermal cooking. Thermal cooking might affect the radical-scavenging activity of the fresh vegetables. The changes in DPPH radical-scavenging activity, the total phenol and ascorbic acid (ASA) contents of various vegetables popularly consumed in Japan were investigated after various thermal cooking processes. In most of vegetables, the radical-scavenging activity and total phenol content tended to decrease during boiling and simmering, and to be retained during microwave heating, pan-frying and deep-frying. However, the ASA content decreased after all cooking processes. Thermal cooking of vegetables did not extensively affect the radical-scavenging activity in spite of loss of ASA, since vegetables contain large amount of phenolic compounds which are stable to heating. These results suggest that the intake of boiled or simmered vegetables with cooking water or microwave-cooked vegetables is recommended to take radical scavenging activity efficiently and to prevent life-style related diseases.   Generally the main component of fishy flavor is considered to be trimethylamine. Our recent studies suggest that the fishy flavor of fresh fishes dose not derive from trimethylamine, but from oxidative products of polyunsaturated fatty acids by lipoxygenase or by autoxidation. Thermal cooking of sardine in the presence of “mirin” suppressed the oxidation of its oil. This effect might be due to the amino-carbonyl reaction products (having strong radical scavenging activity) formed after the reaction of amino acids in sardine and reducing sugars in “mirin” . These results are expected that “mirin” could decrease the formation of fishy flavor of boiled fishes.