To determine the Critical Period for Weed Competition in Sesame crop and predict the total yield losses by weed competition, a field experiment was conducted during season 2023 using three sesame varieties which were Wadaa, Rafidain, and Had by making the field free of weeds by hand for periods of 1, 2, 3, 4, 5 weeks beginning from crop emergence. Then, allowed weeds to grow after these periods until the end of the growing season. Results of the study determined this period by making the field free of weeds for three weeks after emergence depending on acceptable yield losses of 10-12% in comparison to the yield of sesame plants served by weedy-free free throughout the growing season. Sesame yield Losses resulting from weed competition all over the growing season ranged from 66.42 to 95.95% for the three cultivated varieties. Accordingly, this study recommends that weed control must continue from cultivation until three weeks after emergence and not delay it for this period by using mechanical control methods or by using specialist herbicides, which are still effective against weeds until this period to avoid unacceptable loss of the economic yield.