To define preliminary aspects of walnut (Juglans regia L.) callogenesis in indirect propagation systems, this work analyzed callogenic induction in adult leaves of walnut in broadleaf trees (BTM), Murashige and Skoog (MS) Driver Kuniyuki Walnut (DKW) and Woody Plant (WPM) media. Leaf segments of 1 cm², previously sterilized, were placed in each culture medium, supplemented with 21.4 µM naphtalene acetic acid (NAA) and 8.8 µM 6-benzylaminopurine (BAP). A completely random design was used; the experimental unit was a Petri dish with six callus explants. Each treatment was composed of seven Petri dishes. Callogenesis (%), nodular calli (%) and histology of calli explants were evaluated at 4 weeks by staining 10 µm slices with safranine-fastgreen. There were no significant differences (α = 0.05) in callogenesis among evaluated media; but nodular calli percentages were significantly higher in BTM (75%) and WPM (63%). Only in calli obtained in the BTM medium did the histology show the presence of meristematic zones, but without external expression. These results indicate that the medium influences the morphogenic characteristics of resultant callus. Calli produced in BTM presented better morphogenic potential, with meristems at primary stages of organization.