Physic nut (Jatropha curcas) has been considered worldwide as a source of seed oil for the production of biofuel. In Yucatan, Mexico, this crop has been affected by rust caused by Phakopsora jatrophicola (syn. P. arthuriana), an obligate biotrophic fungus, which has become a major constraint in obtaining expected yields. Currently, little is known about the biology of P. jatrophicola. Since there are no previous studies at ultramicroscopic morphology level, we conducted the first Scanning electron microscopy (SEM) examination of this species and a bioassay on J. curcas detached leaves in order to test the spore infectivity. SEM analysis revealed erumpent uredinia with 25 to 35 μm diameter open pore, containing 23 μm length x 11 μm wide equinulated urediniospores. Moreover, spores harvested from Physic nut leaves were able to produce new pustules after 13 days of inoculation on healthy detached J. curcas leaves. These results pro-vide the basis for further researches of this host-pathogen interaction, and may be useful in the development of new molecular methods for diagnostic of this specie.