Abstract: According our study, the contents of total aristolochic acids in the roots and rhizomes of eighteen medicinal Aristolochia species differ greatly. It is, therefore, important to find the way to identify each species in commercial samples.In this paper, the authors deseribed the morphological and histological characters of 18 medicinal Aristolochia roots and rhizomes, viz Aristolochia mollissima, A. tubiflora, A. mollis, A. debilis, A. Contorta, A. fodiana, A. kaempferi f. thibitica, A.elegans, A. hainanensis, A. tagala, A, kaempferi f. heterophylla, A. moupinensis, A. fangchi, A. auscrosgechuanica, A. Kwangsiensis, A. versicolor, A. championii and A. tuberosa, The descriptions are illustrated with line-drawings and photographs. Based on this study, a key for the identification of these roots and rhizomes is also given.