Abstract In many legumes, roots that are exposed to blue light do not form nodules, and blue light induces the biosynthesis of hydrogen peroxide (H2O2). The mechanism of blue light restraining nodulation is poorly understood. Whether H2O2 induced by blue light inhibits nodulation needs to be further studied. In this work, blue light could promote the production of H2O2, activate the expression of LjRbohD and LjRbohE, while inhibit the expression of LjRbohB. After applying exogenous H2O2 and diphenyleneiodonium chloride (DPI), the results show H2O2 induced by blue light represses the nodulation of MG20. The accumulated H2O2 may be generated by LjRbohD, which supported by Q-PCR. Cryptochrome 1A, a blue light photoreceptor, is high expression under blue light. However, there seems to be no direct relationship between LjRbohD and LjCry1A. On the contrary, LjRbohB, a positive governor in the regulation of nitrogen fixation activity in L. japonicus, may be negatively regulated by LjCry1A according to the hairy roots transformation results. Therefore, the mechanisms of regulating the nodulation in L. japonicus by LjRbohB and LjRbohD are quite different under blue light. Keywords: Louts japonicus, accumulated H2O2, blue light, nodulation, LjRbohs.