In order to study the proper heat regime as one of the most important factors for climate change, seeds of mungbean Kawmy-1 variety were exposed to variable extreme waves of temperatures (minimum - maximum oC ) through sowing the seeds on six planting dates, viz: D1 (15 - 22 oC), D2 (18 - 26 oC), D3 (22 - 32 oC), D4 (28 - 38 oC), D5 (27 - 37 oC) and D6 (15 - 22 oC). Mungbean planted in the heat regimes of (18 - 26 oC), (22 - 36 oC) and (28 - 38 oC) could complete their life cycle and produced reasonable yield. Other heat regimes seem to be unfavorable for mungbean since either the seeds did not germinate (15 - 22 oC) or the growth was retarded and in turn no yield was obtained (15 - 22 oC). Mungbean plant sown in the heat regime of (22 - 32 oC) matured earlier, being taller, producing greater number of leaves and branches with heavier weight than that in the other heat regimes. The reduction in minimum temperature by one degree caused reductions in total dry matter plant-1 by 13 and 6% while increasing minimum temperature over the optimum sowing temperature by one degree caused reductions in total dry matter plant-1 by 12.4 and 19.6%. The reduction in minimum temperature by one degree in D2 (18 - 26 oC) caused reduction in seed yield ha-1 by 10.3 and 9.6% per plant and per hectare, respectively. While the reduction in maximum temperature by one degree in D2 (18 - 26 oC) caused reduction in seed yield ha-1 by 6.9 and 6.3 % per plant and per hectare, respectively. Meanwhile, increasing minimum and maximum temperatures by one degree in D4 (28 - 38 oC) caused reduction in seed yield ha-1 by 10.2 and 9.8% per plant and per hectare, respectively. It could be concluded from this study that heat regime is crucial for mungbean planting in Egypt. Mungbean proved to be very sensitive to fluctuations in minimum and maximum temperatures. The most favorable heat regime for mungbean production in Egypt is heat regime of (22 - 32 oC).