Nopal fruits (Opuntia spp.) represent a valuable food in various Latin America countries. Typically, the seeds are discarded. However, they could contain basic components that might enable their use as a nutritional supplement or as another product convenient for the food industry. The objective of this paper was to perform a physical and chemical characterization of the seeds of three species of Opuntia (O. Heliabravoana, O. Xoconostle, and O. ficus-indica) to provide data that will help determine their potential use. Fruits were collected in different municipalities of Hidalgo State, Mexico; its seeds were extracted, dried, and analyzed. The results reveal that, except for small differences, the seeds had similarity in the physical characteristics of density and hardness to abrasion. Due to its relative size and volume, the seed of O. ficus-indica was 2.37 times more voluminous than the smallest seed (O. heliabravoana) and 1.50 times more voluminous than the O. xoconostle seed. The size and morphologies of grains were similar among the species. Due to their relatively high content of oil, fibers, starches and carbohydrates, the seed may represent a nutritional food they result interesting to be evaluated as nutritious food. However, in all the seeds, a substantial amount of lead was found, which is a metal that is non-desirable in any food.