Although a white spot syndrome virus (WSSV) subunit vaccine could significantly enhance the immune response and benefit the shrimp host, its practical application is currently not feasible because of drawbacks in existing expression systems. We generated a transgenic Dunaliella salina (D. salina) strain by introducing the WSSV VP28 gene to produce a novel oral WSSV subunit vaccine. Following transformation of D. salina, VP28 gene expression was assessed by reverse transcription polymerase chain reaction (RT-PCR) assays, enzyme-linked immunosorbent assays (ELISAs), and western blot analysis. The RT-PCR results indicated that the VP28 gene was successfully expressed in D. salina cells. The presence of recombinant VP28 proteins with natural bioactivity was confirmed by western blot analysis and ELISA. Animal vaccination experiments indicated that transgenic D. salina can induce protection against WSSV by oral delivery in crayfish. Our findings indicate that the VP28 gene can be successfully expressed in transgenic D. salina and can be applied as an oral vaccine to protect crayfish against WSSV. We have demonstrated that it is feasible to produce an oral vaccine using D. salina, and thereby provide a new method for controlling other viral diseases in crustaceans.