In order to standardize the titer of polio neutralizing antibody determined by different neutralization tests, the International Standard. Poliomyelitis Antisera have been prepared. Since the supply of the sera is limited, an attempt was made to perpared a national standard serum for the use in Japan. As a result, anti-poliovirus serum type 3 was produced from immunized African green monkeys diluted and distributed into ampoules in 1ml amounts, and freezedried. The reconstituted serum was examined for the protein content. The titer of neutralizing antibody was compared between this serum and the International Standard Serum. From the results of these tests, it was concluded that the prepared serum was suitable for the use as the national standard antipoliovirus type 3 serum, since it contained 40 International units per ampoule.