Two field experiments were conducted at the Experimental station, Faculty of Agriculture, Cairo University, Giza, Egypt in 2005/2006 and 2006/2007 to study the effect of  critical periods of weed competition on Faba bean (Vicia faba L). The experiment consisted of two planting systems one side and both of sides on the ridge with ten treatments: weed-free and weedy periods for three weeks, six, nine, and twelve and the all season. Dominant weed species were weed beet (Beta vulgaris L.), Black mustard (Brassica nigra L.), chicory (cichorium pumilum L.), spring sowthistle (Sonchus olereacus L.), and wild oat (Avena fatua L.) Results indicated that weed removal even once after faba bean emergence substantially reduced the growth of annual broadleaf and grassy weeds after 60 days from sowing and at harvest as compared to weedy throughout all the growing season. But , the most effective treatments were when broadleaved or grassy weeds allowed to grow for 3 or 6 weeks after sowing, recording the highest weed depression values (>70%).  In the second order, the allowing weeds to grow for whole growing season markedly decreased seed yield per plant and feddan than when weeds were removed after 6 or more. Also, seed yield was improved by shortening the period of crop-weed interference through keeping the field free from weeds for the whole season or for 9-12 weeks. (75-78 % in seed yield /feddan over the unweeded and 97.2-98.6% during the first and second seasons respectively). However, sowing faba bean on both sides of the ridge produced higher seed yield per feddan, but the differences did not reach the significance level. Sowing on both side of the ridge reduced fresh weight of both of broadleaves and grasses weeds. However, there were different effects of periods of weed removal importance of based on when it was initiated, being more effective if it was early. Thus, demonstrating that weed interference against faba bean in the early growth periods. Seed yield was reduced from 1.5T/fed. for weed free to 0.5 T/fed. for the weedy treatments. There was a slight difference in the yield between 3 and 6 weeks weed-free periods. However there were insignificant differences between weeds free periods. The critical weed-free period was defined as to prevent yield losses greater than 5% and the critical weed free period was estimated by 40 to 50 days.