In order to expand the acceptability of irradiated foods by public, substantial basic data about the change of nutrient contents during irradiation are needed. The nutrient contents and digestibility of macronutrients such as carbohydrates, proteins and lipids in foods are known to be not significantly influenced by irradiation treatment. However, some of the vitamins among micronutrients are susceptible to irradiation to a large extent depending upon the food composition, food process and storage condition. This study was conducted to investigate change of thiamin in chicken breast, and vitamin C in strawberry and mandarine orange after irradiation. The effects of irradiation at frozen or refrigerated state and the effects of cooking such as heating or micron ave on thiamin contents in chicken breast were observed. Irradiation reduced the thiamin content, however, temperature condition during irradiation was much more important factor to the loss of thiamin contents. In strawberry, vitamin C content was significantly affected by original content or the variety rattler than treatments such as irradiation, heating or microwave. These results indicated that the losses of water-soluble vitamins, especially thiamin or vitamin C, are affected by food temperature during irradiation process and variety or composition of foods rallier than irradiation itself, within an acceptable range of irradiation.