Abstract: A food package for cooking of the food in a microwave oven is formed of a heat-resistant synthetic resin impermeable to oil and moisture and has at least one opening for allowing steam to escape when the internal pressure in the package is increased beyond a certain value by the steam generated during heating. The number of openings and the size of each opening are selected with consideration of the package volume or size and the type of food to be packaged so as to adjustably maintain within the package a pressure and a temperature each of which are within a range of predefined values during cooking in the oven. The package distends with increase of the internal pressure to provide a visual indication that cooking is complete. A method of cooking the packaged food comprises using the described package which adjustably maintains the internal pressure in the package within the range of about 1.00 to about 1.15 atm and the temperature within the range of about 100.degree. to about 105.degree. C.