Abstract: The small G protein Rac1 gene promotes symbiotic nodulation, but the transcriptional regulation mechanism is not clear yet. The promoter sequence of Lotus japonicus Rac1 gene was predicted by bioinformatics and the cis regulatory elements in the promoter were statistically analyzed. The cloned promoter was about 1.8 kb and the recombinant plasmid p1391Z-Rac1Pro fused with GUS was constructed. Positive hairy roots of Lotus japonicus were obtained by agrobacterium mediated transformation method, and the histochemical staining method was further used to study the expressing location of Rac1 gene in the Lotus japonicus. The results showed that the promoter contained not only common transcriptional regulatory elements such as TATA box and CAAT box, but also response elements that regulate signals such as defense, stress, hormones, and illumination. Histochemical staining showed that high expression of Rac1 gene appeared in root hairs, root tips and cortex of nodule primordium.