A packaging bag for microwave oven heating, is manufactured by using a complex film at least one side of which comprises a sealant layer, folding the complex film or placing the complex films one upon another so as to encounter the sealant layers to each other, sealing the peripheral of the overlapped complex films by a main seal part to form a sealed bag, and providing in the bag a region which is isolated from a space for storing contents by a steam port seal part. The steam port seal part surrounds a steam easy permeable element. The lamination strength between the layers of the complex film in hot condition is not less than 1.5 N/15 mm in width, and the seal strength at least at the steam port seal part in hot condition is not more than 28 N/15 mm in width.