The protective efficacy of oral administration of VP28 using Bacillus subtilis as vehicles (rVP28-bs) in shrimp, Fenneropenaeus chinensis, upon challenge with white spot syndrome virus (WSSV) was investigated.The calculated relative percent survival (RPS) value of rVP28-bs fed shrimp was 83.3% when challenged on the 14th day post-administration, which is significantly higher (p < 0.001) than that of the group administered recombinant Escherichia coli over-expressing rVP28 (rVP28-e21). After immunization, activities of phenoloxidase (PO), superoxide dismutase (SOD) and inducible nitric oxide synthase (iNOS) in hemolymph were analyzed. It was found that the supplementation of rVP28-bs into shrimp food pellets resulted in the most pronounced increase of iNOS activity (p < 0.001), but had the least influence on activities of PO and SOD. Besides, in the shrimp orally administered with rVP28-bs, the caspase-3 activity was one-fifth that of the control, though the signs of apoptosis (chromatin margination, nuclear fragmentation and apoptotic bodies) could not be observed by transmission electron microscope (TEM). These results suggest that by oral delivery of rVP28-bs, shrimp showed significant resistance to WSSV and an effect on the innate immune system of shrimp. The remarkably enhanced level of iNOS after rVP28-bs administration might be responsible for antiviral defense in shrimp. Fish & Shellfish Immunology 28 (2010) 49–55. Ling-Lin Fu, Jiang-Bing Shuai, Zi-Rong Xu, Jian-Rong Li, Wei-Fen Li.( Food Safety Key Laboratory of Zhejiang Province, School of Food Science and Biotechnology, Zhejiang Gongshang University, 149 Jiao Gong Road, Hangzhou 310035, PR China Key Laboratory of Molecular Animal Nutrition, Ministry of Education, College of Animal Sciences, Zhejiang University, 164 Qiu Tao North Road, Hangzhou 310029, PR China Zhejiang Entry & Exit Inspection and Quarantine Bureau, Hangzhou 310012, PR China).