6q21 genetic deletion has been frequently detected in extranodal NK/T cell lymphoma, nasal type (EN-NK/T-NT), and PRDM1 is considered as candidate gene. However, direct detection of PRDM1 deletion has not been well documented. We investigated genetic alterations of 6q21 and PRDM1 in 43 cases of EN-NK/T-NT and cell lines by FISH. PRDM1 expression was evaluated by immunohistochemistry and Western blot. The correlation between genetic alteration and PRDM1 expression and the significance in clinic-pathologic were analyzed. Heterozygous deletion of 6q21 and/or PRDM1 was observed in 24 of 43 cases (55.81%) of EN-NK/T-NT including 16 cases (37.21%) for 6q21 deletion and 19 cases (44.19%) for PRDM1 deletion. Similarly, heterozygous codeletion of 6q21 and PRDM1 was identified in NK92 and NKL cells. The heterozygous deletion of 6q21 and/or PRDM1 was correlated with PRDM1 expression. However, genetic deletion of 6q21 and/or PRDM1 was not correlated with clinicopathological features of EN-NK/T-NT, while PRDM1 expression showed positive effect on the outcome of patients as those as disease site, B symptom, and clinical stage. Thus, heterozygous deletion of 6q21 and/or PRDM1 was frequently detected in EN-NK/T-NT and correlated with downregulation of PRDM1. But the prognostic role of genetic deletion needs to be further evaluated in larger cohort.