A hepatitis E virus (HEV) ORF2 peptide expressed in an unfused pattern in E. coli, NE2, can self-assembly into homodimers and oligomers, and the immuno-reactivity of the dimers or oligomers to HEV infected serum is much stronger than monomer, which suggested that some important conformational epitopes be better exposed in dimer or oligomer form. Three Rhesus monkeys were vaccinated with three doses (10 microg/dose) purified NE2 in Freud's adjuvant under a schedule of Od, 10d, and 30d. Specific antibodies can be detected on second week, and on sixth week while virus challenge were performed with 106 PCR titer of virus positive stool suspention, the antibody titer of one monkey was 1: 100 000, the other two were both 1: 20 000. Three monkeys in control group presented typical acute hepatitis E manifestation: increased seral amino transferase (ALT), antibody conversion, and continuous virus excretion in stool. In contrast, the ALT of monkeys in vaccinated group continued to be normal, stool virus had not been detected in one monkey, and presented only a short duration in another two. One NE2-vaccinated monkey serum with antibody titer 1: 20 000 was first incubated with HEV (10(3) PCR titer) for neutralization, then the mixture were used to challenge two monkeys, the results showed that two monkeys in control group continued to excrete virus for more than three weeks, sera antibody conversion, and one monkey presented obvious ALT increase. Both two monkeys challenged with antibody neutralized virus had not detected virus in stool, the antibodies decreased slowly, and ALT continued to be normal. These results suggested that the prokaryotic expression recombinant protein NE2 have good immunogenicity and immunoprotectivity, and should be a good candidate for an effective hepatitis E vaccine.