Epstein-Barr virus (EBV), characterized as an omnipresent virus, has been found able to infect NK cells and leads to NK-cell type EBV-positive lymphoproliferative diseases (EBV-NK-LPDs). We retrospective analyzed 202 EBV-NK-LPDs (including 64 CAEBV-NK, 27 aggressive natural killer-cell leukemia (ANKL), and 111 extranodal NK/T-cell lymphoma (ENKTL)) patients' relationships between EBV DNA copies laboratory test results and clinical features. In CAEBV-NK cohort, EBV DNA loads in either plasma or PBMCs had significant differences between the active state and the inactive state. Receiver operating characteristic curves were used to measure the diagnosis accuracy of EBV DNA copies. After comparing the area under the curve, EBV DNA loads in plasma had significantly higher accuracy in distinguishing disease activation than in PBMCs. Therefore, we propose redefining CAEBV-NK diagnosis criteria as increased EBV DNA copies in plasma (over 7.1 x 10(2) copies/ml) instead of in peripheral blood. In ANKL and ENKTL cohorts, patients who received effective therapy had significantly lower EBV DNA copies in plasma & PBMCs than in those with ineffective therapy. The significant and consistent decline indicated EBV DNA loads in plasma being a more sensitive biomarker in monitoring EBV-NK-LPDs therapy responses. Hemophagocytic lymphohistiocytosis (HLH) can occur secondary to EBV-NK-LPDs, mostly associated with a poor prognosis, so we try to estimate the combination of HLH by monitoring EBV DNA copies. When comparing the Receiver operating characteristic curves of EBV DNA copies, EBV DNA loads in plasma had higher diagnosis accuracy. When the copies level over 4.16 x 10(3) copies/ml, it might indicate combining with HLH.