Abstract: Objective : To observe the expression of protein phosphotyrosine phosphatase SHP-1 in malignant T and NK cell lymphomas. Methods : The expression of the protein phosphotyrosine phos-phatase SHP- 1 in experimental group which contains 30 cases of nasal NK/T cell lymphoma, 20 cases of peripheral T cell lymphoma, 10 cases of angioimmunoblastic T cell lymphoma and 10 cases of precursor T lymphoblastic leukemia and in control group which contains 10 cases of lymph node reactive proliferation, 10 cases of small lymphocytic lymphoma and 10 cases of plasmacytoma was examined by immunohistochemistry staining method. Results : SHP-1 in 70 cases of malignant T and NK cell lymphomas of experimental group was negative, but in 10/10 lymph node reactive proliferations, 5/10 small lymphocytic lymphomas and 5/10 plasmacytomas of control group was positive. There was a significant distinction of SHP-1 expression beween experimental and control groups (χ², P<0.01). Conclusion :Lack of SHP-1 protein expression in various types of malignant T and NK cell lymphoma strongly suggests that SHP-1 gene is potentially an anti-oncogene molecule.