Two WSSV envelope proteins, VP31 and VP33, contain a conserved Arg-Gly-Asp (RGD) sequence. In order to investigate the role of the RGD motif, wild-type and RGD-mutated VP31 and VP33 were recombinantly expressed in E. coli. The cell adhesion ability of the proteins was investigated in crayfish haemocytes using a fluorescence assay. The results showed that recombinant wild-type VP31 and VP33 had cell adhesion activity, and the RGD motif in VP31 was required for cell adhesion, which could be inhibited by an RGDT peptide. In contrast, the interaction of VP33 with cells did not require the RGD motif. These data indicate that the RGD motif plays an important role in the interaction between VP31 and host cells.