The incidence of Australia antigen (HAA, HBsAg), a known market for hepatitis B virus (HBV), is expected to e high, esp. in the subclinial type. It is well known that the incidence of HAA positivity among the patients with specific diseases and group of blood donors is relatively high in adult age group. But since there is less research for the incidence of HAA in Pediatric age group, the necessecity of investigation of its incidence is required properly. Thirteen from 306 children (4.58%) who were selected randomly among hospitalized patients from Feb., 1975 to April, 1977, were positive for HAA in their serum sample tested by the apgar gel diffusion method. The incidence of HAA was higher (6.54%) in male than in female(0.99%) patients and a trend toward increments was noted with age.