The heating performance of prototype variable power control units attached to two domestic microwave ovens, 500W and 700W, was investigated. The units employed the phase control method where rated voltage was obtained by switching AC supply at a particular angular position on the sinusoidal voltage. In order to create experimental conditions employed in a previous study, Sydney tap water (50mL) was heated at a 10% power level in the 500W oven. Water boiled at 10min in both experiments. However, the precision and control of the heating was greatly improved with addition of the control unit. A disinfecting solution (50mL) and a tissue fixative (10mL) were included for experiments with the 700W oven. A power level of only 1% was sufficient to maintain the temperature of the fixative at low temperatures (30-40°C) where many biological reactions occur. The present results indicate that microwave heating power can be controlled by the variable power control method. This will make temperature control possible through the provision of an electronic feedback loop which links a thermocouple with the power control unit.