Fourteen genes encoding E2(LjE2) in Lotus japonicus genome were identified based on the sequence of E2 in Arabidopsis to study the function and mechanism of ubiquitination in the process of symbiotic nitrogen fixation in legumes. Among them,eleven LjE2s were cloned to construct the fusion expression vectors pETLjE2s:His. Ten LjE2 proteins were successfully expressed and purified under the prokaryotic expression system. The results of ubiquitination in vitro and Western blotting showed that nine LjE2s had ubquitinconjugation enzyme activity and one had no detectable ubquitinconjugation enzyme activity.