Only about 4% of Egypt's total area is agricultural land and this area has one of the highest population densities in the world. Since the early 1960s, vast areas in the Egyptian deserts (Western, Eastern and Sinai) were subjected to land reclamation; private and government schemes. This human interference causes the weedy species to replace the wild plant species in these reclaimed areas which are considered as transitional habitats between the old cultivated land and desert. The invasive species in the new agricultural lands cause serious problems that require attention to be paid to the negative impacts of plant invasions on ecosystems and gene pools The aim of this work is to recognize the main agro-ecosystems in the reclaimed lands along the northern sector of the Nile Valley in Egypt, and to study the relationship between crops and their weed flora. It attempts also to determine the prevalence and agro-ecological distribution of weed species in major crops in different agro-ecosystems, and to assess the influence of some environmental factors on weed species composition and distribution.