The cytoskeleton such as microfilaments and microtubules play important roles in the mechanism of viral infection, replication release and virus-host cell interactions. In this study, the Singapore grouper iridovirus (SGIV) particles were purified and the viral envelopes were separated from the viral particle by detergent dissolution. The envelope proteins were identified by 1-DE-MALDI TOF and LC-MALDI TOF workflows. Except for viral proteins, 7 host proteins were found to exist in the envelope component including actin. Thus, these host proteins were co-purified with the viral particles. Actin was proved to exist with the envelope by Western-blot. Further, it was observed that the actin proteins existed on the surface of the virus particles by immnoelectron microscopy, suggesting that host original actin is packed to viral particle when SGIV is matured and finally released from the host cell. Actin may be assembled in the viral surface when virus is budding or it is specifically adhered to the viral envelope. This makes actin co-purified with the envelope proteins. Further studies indicated that the virus-infected cell turn round and the viral particles were co-located with the microfilament on the cell surface. This suggested actin was involved in viral release. When the SGIV was released from the cell, the virus obtained the cell membrane as its envelope, which was observed by electron microscopy. It was speculated that actin was specifically packed to the surface of the viral particle when SGIV was released. Together, actin played important roles when the viruses were released from the host cells.