AbstractThis study was carried out to evaluate the effect of heat and cold on the microorganisms existing in prawn. Roasting for 5 min, boiling for 10 min and storage at − 18 °C for 10, 20 and 30 days were applied on raw prawn to study the effect of each treatment on the bacterial load.The average counts of APC (aerobic plate count) at 25 °C and 0 °C,Enterobacteriaceae, ColiformsandStaphylococciwere 1.3 × 107, 6 × 104, 3 × 104, 2 × 102and 3 × 103organisms per gram raw prawn sample, respectively, then reduced to 104, 8 × 102, 3 × 103,<3 and 3 × 102organisms per gram roasted prawn in shell, respectively. Such counts were more reduced in roasted peeled samples. Boiling reduced the average counts of APC at 25 °C and 0 °C,Enterobacteriaceae, ColiformsandStaphylococcifrom 8 × 108, 2 × 1052 × 107, 3 × 10 and 3 × 104organisms per gram raw prawn sample to 2 × 105, 3 × 103, 2 × 102,<3 and 4 × 102organisms, respectively. Concerning freezing storage, it could be observed that the average counts of APC at 25 °C and 0 °C,Enterobacteriaceae, ColiformsandStaphylococciwere reduced from 4 × 107, 5 × 105, 3 × 105, 103and 3 × 102organisms per gram raw sample to 5 × 104, 103, 3 × 102, 10 and<2 × 102organisms per gram af