The present study deals with some features of ecology and phytochemistry of three Amaranthus species, namely: Amaranthus graecizans, A. lividus and A. viridis which are naturally growing in the Nile Delta region of Egypt. The composition of weed vegetation in the present investigation is classified by cluster analysis into four groups: group A is codominated by Amaranthus graecizans and Portulaca oleracea, group B is codominated by Amaranthus lividus and Cynodon dactylon, group C is codominated by Alternanthera sessilis and Echinochloa crus-galli and group D is codominated by Aster squamatus, Conyza bonariensis and Paspalum disticum. The ordination of the sampled stands applied by Detrended Correspondence Analysis (DCA) indicated that, the recognized vegetation groups are markedly distinguishable and having a clear pattern of segregation on the ordination plane. The application of the Canonical Correspondence Analysis (CCA) showed that, soil texture, porosity, water-holding capacity, bicarbonate, sodium, soil reaction (pH), organic matter and electrical conductivity are the most effective soil variables which correlate with the distribution and abundance of weed vegetation in the study area. The seed germination under different levels of salinity, light, temperature and humidity is studied for the three investigated species. Phytochemically, the mean values of moisture, ash, total nitrogen, protein, total lipids, soluble sugars, glucose, sucrose, polysaccharides and total carbohydrates were determined. The elementary analysis together with qualitative and quantitative analyses of 16 amino acids were also carried out in the investigated plant species.