To evaluate the potentials of growth and nitrogen (N) fixation of genus Crotalaria used as green manure, interspecific differences in dry matter production, root nodule formation, and N uptake among several species were investigated in field and pot experiments at Osaka, Japan. C. juncea, C. spectabilis, C. pallida, and C. incana exhibited vigorous vegetative growth, expanding leaf area and branching, and they began to flower in mid-July to early August. C. juncea had a high dry weight and a great N content at early growing stage probably due to faster root nodule formation. On the other hand, C. pallida grew slowly at the early stage due to slower nodulation, but had a high N content at the late stage. Incorporation of each species provided a large amount of N necessary for the succeeding wheat crops. Several indicators for rapid decomposition of the plants, such as total C, N and lignin contents, were investigated, and the possible increases in N supply and growth inhibition by incorporation to wheat crops were discussed. N-absorbing activity of C. juncea grown under the excess N condition (70 gN m^-2) was also evaluated. The proportion of fixed N to total N was less than 1%, and the C/N ratio was significantly lower than that in Z. mays, suggesting that this plant species could be also useful as a cleaning crop.