Abstract: Objective : To analyze the EBNA1 IgA antibody level of normal and NPC subjects in high-risk area for new diagnostic criteria to improve diagnosis. Methods : EBNA1 IgA antibody levels of 780 normal and 104 NPC sera were tested using ELISA. Two diagnostic criteria were obtained from sensitivity and specificity data: a) lower equivocal limit (r0D=1.10) where sensitivity was 95%; b) upper equivocal limit (r0D=1.85) where specificity was 95%. Results : The range and distribution of EBNA1 IgA antibody levels were broad with those of normal subjects (0.093-4.726, mean=0.850 (0.637) overlapping those from NPC subjects (0.235-3.721, mean=2.241 (0.875). However, the antibody levels was significantly high in NPC subjects (t=18.5, P<0.001). Based on the diagnostic criteria, three diagnostic categories were established: 1) Positive; 2) Doubtfully positive; and 3) Negative. Percentage of NPC subjects falling into the three diagnostic categories was 75.13%, 17.44% and 7.44% respectively and of normal subjects, 4.81%,17.31%,77.88% respectively. Conclusion : Due to the broad distribution and overlapping of antibody levels between normal and NPC subjects in the area of high incidence, it is important to have diagnostic criteria that will categorize those with equivocal results to minimize misdiagnosis. The three diagnostic categories established in this study will enhance the detection and will be beneficial for physicians in their clinical diagnosis.