an improved heating time control apparatus and method thereof for a microwave oven capable of advantageously computing an optimum cooking time without controlling the amount of food to be cooked . the invention includes : a sensor for detecting a predetermined physical , i . e . parameter , variation of the food being heated and for converting the physical variation into a predetermined electrical signal ; a converter for comparing the physical variation outputted from the sensor with an initial value and for converting the physical variation into the varying ratio which is referenced to the initial value ; a heating time detecting circuit for setting a first heating time obtained while the varying ratio outputted from the converter becomes a minimum value and for setting a time obtained while the varying ratio varies from the minimum value to a predetermined value as a second heating time ; an operator for computing a predetermined value varied as much as a predetermined value in determining the second heating time using the minimum value of the varying ratio outputted from a storing circuit , the first heating time and a first coefficient outputted from the storing circuit and for producing a third heating time using the first and second heating times outputted from the storing circuit and a second coefficient outputted from a coefficient storing circuit ; and a counter for counting the first and second heating times outputted from the heating time detecting circuit and a third heating time outputted from the operator .