Abstract: This invention provides a packaging bag for a microwave oven capable of allowing vapor generatetd during microwave heating to escape surely, which comprises a bag body comprising an upper side sheet portion and an underside sheet portion and an upper fin seal portion formed on the upper side sheet portion formed on the upper side sheet portion, wherein said upper fin seal portion is formed of heat-sealed laminated films comprising an inner layer film and an outer layer film, and wherein said upper fin seal portion comprises a non-sealed portion connecting with a container portion of the bag body, a projected portion projected from an inside end of a heat-scaled portion, and a weakly joined portion having a peel strength of 0.1 to 15 g/15 mm width formed between the inner layer film and the outer layer film at least surrounding the projected portion and connected with an outside end of the upper fin seal portion.