Some plant families (Fabaceae,Asteraceae, Brassicaceae, Poaceae, Solenaceae, Cucurbitaceae....) have different allelopathic capability to produce and exude allelochemicals into their environments to suppress the growth of annual weeds in their surrounding area. In this study, wheat (Triticum aestivum L.), corn (Zea mays L.) and their associated annual weeds were exposed to the allelochemicals arised from their previousing crops during the crop rotation. The summer crops prior to wheat were maize, sorghum, panicum, alfalfa, cowpea, sunflower. While the winter crops prior to maize were safflower, barley, canola, rye, oat, wheat, respectively. For this target two field experiments were conducted at Maryout Experimental Station, DesertResearchCenter during 2003-2005 winter and summer seasons. Weed species associated to wheat exhibited substantial significant reduction in its fresh and dry weights as a result of growing wheat subsequent to maize,  sorghum, alfalfa, sunflower,  panicum and cowpea, respectively. Wheatgrain yield and biological yield showed significant increases with the same species order after the decomposition period  of crop residues. . The fresh and dry weights of weed species associated to maize were reduced significantly by sowing maize subsequent to wheat, barley, oat, rye and safflower, respectively. Maize grain yield and biological yield showed significant increases with the same species order, respectively. The families of Poaceae and Fabaceae was the best families that were used before wheat and maize in control of annual weeds associated with crops compared to other families. Read phonetically This work aimed to study the allelopathic capability of some plant families that precede each of wheat or maize in the agricultural cycle, to control the annual weeds associated to wheat or maize and same time to increase their growth and productivity