Foot-and -mouth disease to pigs is serious recently around the world. "Vaccination prevention" is still an important policy. OIE specifies 10,000 TCID50(0.2 ml) of virulent virus for challenge test in pigs to test the potency of FMD vaccine by intradermal route inoculating the virus in the heel bulbs of one foot or by intramuscular route administering into one site of the neck behind the ear. Convenience and speediness are available in the process of potency test of commercial FMD vaccine. We selected the route of "administering into one site of the muscular part of the neck behind the ear" because of convenience and speediness. However, it was difficult to infect control pigs even up to 100,000TCID50, so we changed the challenged virus from cell-passaged strain to suckling mice-passaged one, measured its PID50 (pigs median infected dose) and defined the virus challenge dose as 1000PID50. Meanwhile, we arranged the number of control pigs from two to three for easy evaluation.