Abstract: Temperature caused a significant change in the bioenergetics of the two forensically important flies namely, the housefly Musca domestica vicina Macquart and the blow fly Lucilia sericata Meigen in the laboratory under different constant temperatures. The oxygen consumption of both species increased with an increase in the larval weight at all tested temperatures. Conversely, as the weights of both species increased, the oxygen consumed per mg fresh or dry weights decreased. The pupal respiration followed the U-shaped curve. The calculated temperature coefficient (Q10) values were not very high for all stages of both species at lower temperature. The instantaneous rate of assimilation of the feeding larvae of both species increased with increasing weight and age. The instantaneous growth efficiency and the cumulative growth efficiency values at all tested temperatures were higher for L. sericata than M. domestica. The oxygen consumption and food assimilation are age markers of the immature stages of these two forensically important flies and can be used easily in the accurate estimation of the postmortem interval.