Objective: To investigate the expression of tumor suppressor gene PTEN in hematologic malignancies and its clinical significance, as well as to explore its relativity with Acute Leukemia (AL) and role in pathogenesis and development of AL. Methods: The cases included 74 patients with hematologic malignancies: 35 patients with Acute Leukemia, 20 patients with Myelodysplastic Syndromes(MDS), 13 patients with chronic myeloid leukemia(CML), 6 patients with myeloid proliferation disease(MPD). We took 24 patients with non-hematologic malignancies and 10 cases of normal human bone marrow as control. The expression of PTEN in the bone marrow mononuclear cells was detected by SP immunocytochemical staining. We also did analysis on its relativity with clinical parameters and follow-up study on disease prognosis. Results: In control groups, the positive expression rate of PTEN in non-hematologic malignancies patients (83.33%) is lower than that in normal (90.0%), which was no significant difference (p>0.05). The positive rate in hematologic malignancies patients is 57.14%, which shows significant difference from control (P<0.05). There are no significant difference (0.05>P>0.01) between positive expression rate of PTEN in AL-CR(63.16%) and control, as well as that in AL initial treatment (55.17%) and AL-CR. The positive rate is 70.0% in MDS group, 73.68% in MPD groups. Both MDS-RAEB(53.33%) and MDS-AL (53.85%) shows significant difference from normal control (P<0.05) but no significant difference from AL in initial treatment (P>0.05). PTEN Low expression has certain relativity with peripheral blood leukocyte count and the proportion of progenitor cells bone marrow in pathogenesis (r≈0.53). CML-AL shows positive relativity with MDS-RAEB transforming AL (r≈0.53). Conclusion: There is abnormal expression of tumor suppressor PTEN gene in Acute Leukemia, and PTEN may have some relativity with pathogenesis of the AL, which suggests that PTEN has certain significance in pathogenesi