The present thesis is devoted to investigate the chemical composition of some seeds of three different species, each include two varieties or cultivars, representing three genera and three families as follows:- (From Malvaceae, cotton seed cvs. Giza 86 and Giza 66, Solanaceae, tomato seed vars. Pyriforme and grandifolium and Brassicaceae, rape seed cv. Pactal and var. Tower). The seeds under study even cultivars or varieties were obtained from The Seed Bank Of Flora and Phytotoxonomy Research Department (CAIM), Horticultural Research Institiute (HRI), Agricultural Research Center (ARC). The aim of the present work was to clearity the importance and the significance of the seed chemical composition as critera in taxonomic aspects. The different seed chemical composition of the studied taxa are presented in forms of cumulative tables and plates. The general chemical analysis including lipid content, protein contents, total carbohydrates, mineral constituents, amino and fatty acids were determined in seed plant sample of the studied cultivars and varieties to facilitate the separation of the studied taxa, as well as, their use as criteria in taxonomic treatments. It is quite clear that, different chemical compositions and their amounts could be considered as diagnostic features that make differentiation between the studied cultivars and varieties easier and more effective.