Because cattle are the most important economic and susceptible cloven-hoof animal, we designed an experiment to verify whether this produced antigen can be used for preparing a cattle FMD vaccine. We followed the bovine potency test protocol described by the OIE to test this subunit vaccine potency. We used 1/30 diluted dosage to vaccinate five cattle and two controls were vaccinated with vaccine prepared from BmBacPAK-6's. By two weeks post vaccination, the antibody level of the five vaccinated cattle reached a high titer. The antibody level has some ascension but maintained thereafter two weeks, while the control group maintained lower than titer 8. After virulent homologous virus challenge, four of the five were considered protected, and one delayed the disease and ease the clinical symptom, but two unvaccinated cattle developed lesions on all the feet and in the inside of mouth on the second day. Cell-mediated -immune response was probably involved in the protection: that would explain why animal 45 has the same neutralizing antibody titers as 122 but is not protected. This demonstrated that the expression products from silkworm-baculovirus expression system were immunogenic as well. Based on above result, we did the PD50 test to assess the bovine potency of the subunit vaccine. When employed for routine prophylactic use, the vaccine should contain at least 3 PD 50 per dose for cattle by OIE recommended. The result showed the subunit vaccine potency could get 6.34 PD 50 a dose for cattle. This leads to a conclusion that it is feasible to use the silkworm-baculovirus expression system for FMD vaccine production. 