Abstract: Two leguminous tree species i.e., Acacia dealbata and Acacia mearrnsii were observed in semi - sealed tube with sterilized non -nitrogen solution, and nodule bacteria were isolated from root nodules of both these two species by following the method suggested by Vincent(1970).The preliminary determination indicated that the nodule bacteria were Rhizobium spp..Backward inoculation of bacteria colony 03 -A -1 from Acacia dealbata was done to yang seedlings of the same tree species and root nodules were obtained, and bacteria colony 03 -D -2 from Acacia mearrnsii was backward inoculated to seedlings of the same tree species and the same result was obtained.It was indicated that the colonies of 03 -A -1 and 03 -D -2 should be the nodule bacteria of these tree species.