Primary testicular NK/T-cell lymphoma is an extremely rare entity progressed rapidly.The aim of this study was to examine clinical and pathological features of primary testicular NK/T-cell lymphoma and to investigate the effective diagnosis and prognosis.In this paper,the two cases of primary testicular NK/T-cell lymphoma were observed by light microscopy,immunohistochemistry and examined by in situ hybridization for Epstein-Barr Virus(EBV) DNA and the literatures were reviewed.The two patients respectively present with bilateral and right-side painless testicular enlargement.The morphology of neoplastic cells of case 1 were small to medium,tumor cells of case 2 were small,medium and large mixed.The tumor cells grew diffusely with irregular and distort nuclear,destructed the organizational structure of the normal testis,and damaged blood vessels,meanwhile,coagulation necrosis was exist.Immunohistochemical staining of neoplastic cells showed positive for CD45,CD2,CD56,CD3ε(cytoplasm staining pattern),CD45RO and Granzyme B,and negative for CD57,CD20,CD79α,CD30,CK,MPO,TdT,Bcl-2 and PLAP were negative.In addition,the EBV DNA was detected in the lymphoma by In situ hybridization.In conclusion,the expression of CD56,CD3ε,and Granzyme B associated proteins and EBV examination by in situ hybridization play a vital role in diagnosis and differential diagnosis of primary testicular NK/T-cell lymphoma. Primary testicular NK / T-cell lymphoma is an extremely rare entity progressed rapidly. The AIM of this study was to examine clinical and pathological features of primary testicular NK / T-cell lymphoma and to investigate the effective diagnosis and prognosis. In this paper, the two cases of primary testicular NK / T-cell lymphoma were observed by light microscopy, immunohistochemistry and examined by in situ hybridization for Epstein-Barr Virus (EBV) DNA and the literatures were reviewed. The two patients respectively present with bilateral and right- side painless testicular enlargement. The morphology of neoplastic cells of case 1 were small to medium, tumor cells of case 2 were small, medium and large mixed. the tumor cells grew diffusely with irregular and distort nuclear, destructed the organizational structure of the normal testis , and damaged blood vessels, meanwhile, coagulation necrosis was exist. Immunohistochemical staining of neoplastic cells showed positive for CD45, CD2, CD56, CD3ε (cytoplasm st aining pattern), CD45RO and Granzyme B, and negative for CD57, CD20, CD79α, CD30, CK, MPO, TdT, Bcl-2 and PLAP were negative.In addition, the EBV DNA was detected in the lymphoma by In situ hybridization. In conclusion, the expression of CD56, CD3ε, and Granzyme B associated proteins and EBV examination by in situ hybridization play a vital role in diagnosis and differential diagnosis of primary testicular NK / T-cell lymphoma.