Abstract: 21 species of tree legumes, which belong to genera Cassia, Cercis, Delonix, Gymnocladus, Gleditsia (Caesalpinioideae), Albizia, Samanea, Calliandra, Pithecolobium, Acacia, Adenanthera (Mimosoideae), Robinia, Amorpha, Wisteria, Sophora and Dalbergia (Papiljonoideae), have been examined for nodulation under pot culture and field conditions with unsterilized leguminous rhizospheric soil. Out of these only 12 tree legumes were found to be nodulated. It was interesting to note that the two species of Cassia and one each of Gleditsia, Cercis, Delonix, and Gymnocladus neither nodulate in field nor does it under pot culture conditions. All of them belong to the same sub-family of Caesalpinioideae. It was surprising that Japanese Pagoda-tree (Sophora japonica), a common species of tree legumes in Nanking, did not nodulate, either. There are four species of tree legumes first reported hereunto, and two species are conflicting with other authors heretofore.Root nodule bacteria from tree legumes were isolated following the method suggested by Vincent (1970). Isolates of Rhizobium were further purified and maintained on YEMA slants in culture tubes. In general morphological characteristics of the cells and colonies, all the isolates were confirmed to be typical Rhizobium. Advanced confirmation of isolates have been made by proper plant inoculation tests. Rhizobia from these nodules generally are slow-growing strains of the cowpea-soybean-lupine type. Host-infection studies of the members of the tree legumes and Vigna studied to date have verified these plants and their microsymbionts as members of the cowpea miscellany. With few exceptions, the 9 strains of Rhizobium were able to nodulate all the tree legumes tested. Eventhough, an artificial inoculation of Rhizobium pure culture from some nodulated tree legumes was carried out, all the Caesalpiniaceous species failed to nodulate. Pseudonodulation of some Caesalpiniaceous plants and Red Sandal-wood (Adenanthera pavonina) may be a consequence of treating plants with growth regulatory chemicals such as 2,4-D; such hypertrophies are blunt, deformed modified rootlets.