Betanodaviruses are the causative agents of viral nervous necrosis (VNN), a serious disease of cultured marine fish worldwide. To control this disease, vaccines of subunit capsid proteins (recombinant proteins or peptides), inactivated viruses, and virus-like particles (VLPs) were developed. VLP, which is highly similar to the wild-type virus in virion structure and contains no viral genome, was proved as one of the good and safe vaccines that can activate humoral immune response in the long term and induce cellular and innate immunities in the early stage post-immunization. The VLP vaccines can be expressed in vitro either by Baculovirus-based or yeast-based eukaryotic system or by bacterial expression system. In this chapter, the prokaryotic expression and the subsequent purification of VLP of betanodavirus orange-spotted grouper nervous necrosis virus (OGNNV) are presented.