Antibody titer and immunoprotection induced by VP7 subunit vaccine were explored in the present study. The gene of the grass carp reovirus(GCRV) coding the outer capsid protein VP7 was amplified and inserted into prokaryotic expression vector pET-28a(+) to obtain pET-VP7, which was transformed into BL21(DE3) for expressing. SDSPAGE showed that the expressed VP7 protein had a molecular weight of about 34 000 and Western Blot detection indicated good immunoreactivity of the protein. After denaturation and renaturation, the expressed VP7 protein was used to immunize grass carp based on three doses: 0.5, 1.0 and 2.0 mg, which was mixed with an equal volume of aluminum hydroxide adjuvant except the control. Indirect agglutination detection showed that antibody against VP7 protein was produced in the immunized groups. Challenge experiment with GCRV showed that 90%, 85% and 90% protection were achieved in groups respectively immunized with 0.5, 1.0 and 2.0 mg of the expressed VP7 protein and no protection was shown in the control group which demonstrated that the VP7 subunit vaccine made here had good immunoprotection against GCRV.