Morphological characteristics and chemical composition of seeds of four species of Opuntiagenus endemic to the Samalayuca Valley were evaluated in this study. Morphology andchemical composition of the four species were clearly different. Seeds of O. polyacanta var.arenaria presented the highest values of area, length and width. However, O. phaeacanthashowed the highest values in palmitoleic acid (1.34 ± 0.12%), stearic acid (5.60 ± 0.47%), oleicacid (19.42 ± 1.04%), alpha linolenic acid (2.42 ± 0.33%), arachidic acid (0.61 ± 0.11%), andeicosenoic acid (1.74 ± 0.36%); but, this species showed the lowest values in linoleic acid(54.35 ± 2.91 %) content. In conclusion, seeds of O. phaeacantha could be an important newsource of health-promoting polyunsaturated fatty acid, and its use in arid and semi-arid regionsshould be encouraged.