Abstract： Objective:To explore the characteristics of plasma Epstein-Barr virus (EBV) DNA in primary infection in pediatric cases.Methods:The laboratory and clinical data of 571 children diagnosed with EBV primary infection in Children′s Hospital of Fudan University during September 1 st, 2017 to September 30 th, 2018 were retrospectively analyzed. According to the results of plasma EBV DNA, they were divided into positive group and negative group. According to the EBV DNA, they were devided into high plasma virol load group and low plasma virol load group. The Chi-square test, Wilcoxon rank sum test were used to compare the differences between groups. Results:Among the 571 children with EBV primary infection, 334 were males and 237 were females. The age of first diagnosis was 3.8 (2.2, 5.7) years. There were 255 cases in positive group and 316 cases in negative group. The percentage of cases with fever,hepatomegaly and (or) splenomegaly, elevated transaminase in the positive group were higher than those in the negative group (235 cases (92.2%) vs. 255 cases (80.7%), χ 2=15.22, P<0.001; 169 cases (66.3%) vs. 85 cases (26.9%), χ 2=96.80, P<0.001; and 144 cases (56.5%) vs. 120 cases (38.0%), χ 2=18.27, P<0.001; respectively).In the positive group, 70 cases were followed up for 46 (27, 106) days, 68 cases (97.1%) turned negative within 28 days, with the exception of 2 cases (2.9%) developed chronic active EBV infection by follow-up revision.There were 218 cases in high plasma viral DNA copies group and 37 cases in low copies group. More cases presented with elevated transaminases in the high plasma viral DNA copies group than those in the low group (75.7% (28/37) vs. 56.0%(116/207), χ 2=5.00, P=0.025).Both the positive rate of EBV DNA in peripheral blood leukocytes (84.2% (266/316) vs. 44.7% (255/571), χ 2=76.26, P<0.001) and the copies of EBV DNA (7.0×10 7 (1.3×10 7, 3.0×10 8) vs. 3.1×10 6 (1.6×10 6, 6.1×10 6) copies /L, Z=15.23, P<0.001) were higher than that of plasma. Conclusions:In immunocompetent pediatric cases diagnosed as EBV primary infection, cases with positive plasma EBV DNA were prone to have fever, hepatomegaly and (or) splenomegaly, and elevated transaminase than those with negative plasma viral DNA. The plasma EBV DNA usually turns negative within 28 days after initial diagnosis.Most cases with high viral load in plasma showed elevated aminotransferase.