The effects of microwave treatment on the perservation of foods, such as a seaweed soup and sea stoned radish shreds, were studied. Microwave treatment of microbial cell suspensions revealed that viable cells decreased dramatically when heated to 6. However, it was unlikely that microwave treatment to 60 is enough to decrease the viable cell counts efficiently in a seaweed soup and radish shreds. It was thought that microwave heating to at least 7 as a final temperature was an important factor to reduce microbial cell counts in foods. When foods were heated to 7 with a repetitive 15 sec "on" followed by 30 sec "off", no big differences were observed in viable counts during storage at 2 for 3 days, as compared to those treated with a full power. The microwave treatment with three stages was designed to solve problems associated with variations depending on food volumes and difficulties of heat diffusion in a solid food to be irradiated with a microwave oven. The three stage method was found to have a similar efficiency in the reduction of viable cell counts in foods to microwave treatment at a full power and to conventional methods, such as water bath heating or boiling for 3 min with a gas range.in with a gas range.