Several aspects of the ecology of Jameson’s green mamba Dendroaspis jamesoni jamesoni (Traill, 1843), a large-sized arboreal elapid snake, are studied in southern Nigeria. This species is common and widespread in the region studied. On the basis of the analysis of both the habitats of capture of the various specimens and the results of a logistical regression model, it seems that this species inhabits a wide variety of habitats (including secondary forest patches and the plantation-forest mosaic), and that its local distribution is not influenced by the presence of any macrohabitat parameter. Green mambas were observed both in the dry and in the wet season, without any statistical bias toward a particular season. Adult sex-ratio was approximately 1 : 1. Males were significantly longer than females. All adult mamba dietary records involved warm-blooded prey (mainly birds), whereas young mambas fed also upon lizards and toads. Nearly all the prey eaten by adult mambas were arboreal, and thus there was no support for the recent hypothesis that adult mambas develop an orientation to forage on terrestrial rodents. Male-male combats and matings were observed in December, January, and February (dry season), and gravid females were collected in April, May, and June (wet season). Females produced 7-16 eggs (mean 10.9), and litter size was positively correlated with maternal length.