Similarity of the weed seeds with the crop seeds is of great importance as it is one of the important means of crop-weed contamination. In any crop presence of weed seeds, which are similar in size, shape and weight to those of crops (the seed mimicry), can affect the quality as well as the yield of the crop. Seed mimicry was studied in two groups of plants, viz. Argemone-Brassica-Cleome and Vicia-Lathyrus groups, through a detailed study of their seed morphology. The seed morphology was studied with the help of a stereoscopic microscope under 100 to 200 time’s magnification. The study clearly revealed the similarities in the seed characters, viz. seed shape, size, colour and 1000 seed weight along with some other similar seed characters. Ofcourse, there were differences in some of the seed characters like hilum, raphe, funicle, wall type etc based on which the weed seeds could be separated from their associated crop seeds. The study will also facilitate the identification of seeds for quarantine measures as well as for seed certification.