Extranodal natural killer (NK)/T-cell lymphoma, nasal-type (ENKTL) is a clinically heterogeneous disease with poor prognosis and requires risk stratification in affected patients. Recent studies have shown that Ki-67 may serve as a prognostic marker in certain types of lymphoma. We analyzed Ki-67 expression and its correlation with prognosis in 182 patients with ENKTL from January 2002 to June 2013. The patients were classified into two groups through a median value: low (<60%) versus high Ki-67 (≥60%). High Ki-67 expression was more common in patients with B symptoms (p=0.02), bulky disease (p=0.001), and extraupper aerodigestive tract NK/T-cell lymphoma (p=0.001). High Ki-67 expression was significantly associated with poor overall survival (p<0.0001) and progression-free survival (p<0.0001). For patients with low-risk IPI or KPI, Ki-67 at diagnosis could contribute to distinguish patients with favorable outcomes from those with poor outcomes. The results of multivariate analysis showed that the high Ki-67 expression is an independent prognostic factor for overall survival and progression-free survival. (OS, p=0.001; PFS, p=0.003). Our data showed that Ki-67 is an effective prognostic indicator of survival in ENKTL patients. This prognostic index may be helpful in identifying high-risk patients with ENKTL.