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 pETLjE2s: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 ubquitinconjugation enzyme activity and one had no detectable ubquitinconjugation enzyme activity.