Although extranodal NK/T cell lymphoma (ENKTCL) is consistently associated with Epstein-Barr virus (EBV) infection, the manifestation and prognostic value of serum EBV antibodies still remain unknown. One hundred and forty-one patients with ENKTCL were evaluated for serum EBV EA-IgA and VCA-IgA antibodies levels in the past 24 years in our institution. Their correlation with clinicopathological features, plasma EBV DNA load, and patients' outcomes was analyzed. EBV EA-IgA ae1:10 and VCA-IgA ae1:160 were found in 18.4 and 16.3% of patients, respectively. They correlated with adverse ENKTCL profile and inferior overall survival (OS) and progression-free survival (PFS). EA-IgA ae1:10 was an independent prognostic factor on OS (RR = 2.276, p = 0.008) and associated with lower complete response (CR) rate (34.8 vs 70.6%, p = 0.001) and higher relapse rate in CR patients (62.5 vs 34.7%, p = 0.016). In subgroup analysis, both EA-IgA ae1:10 and VCA-IgA ae1:160 significantly correlated with inferior OS and PFS in patients with stage I/II, IPI score 0-1, plasma EBV DNA (+), and CR. Patients with plasma EBV DNA (+) and EA-IgA ae1:10 (or VCA-IgA ae1:160) had significantly shorter periods of OS and PFS in comparison with other corresponding groups. Elevated serum EBV EA-IgA and VCA-IgA levels were related to adverse ENKTCL profile and correlated with poor treatment response, early relapse, and poor prognosis in patients with ENKTCL. These findings provide convincing evidence for the use of serum EBV EA-IgA and VCA-IgA antibodies for risk group stratification and prognostic prediction in ENKTCL.