Study on EBV exposed Tay ethnic by ELISA technique in Cao Bang. 130 healthy people who had age range between 10 to 60 year old were enrolled in study on IgO/VCA concentration. All of subjects were 3 consecutive generation of Tay ethnic who lived in Trung Khanh, Cao Bang province. The findings were as followed: IgO/VCA concentration or = 5UI/ml was 89.2 percent. The differentiation of IgG/VCA between 2 sexes was not significant (p0.05). The concentration of IgG/VCA 5UI/ml was most frequency in 10-15 year-old group. The differentiation of IgO/VCA between age group was not significant (p0.05). In the group had ENT disease, IgO/VCA concentration between 5-50UI/ml was highest (46.7 percent) and 5UI/ml was lowest (7.8 percent). In group without ENT disease, IgG/VCA concentration between 5-50 UI/ml was also highest (57.5 percent) and there was no case with concentration 200UI/ml. Regarding to ENT disease, the differentiation of IgO/VCA was significant (p0.05).