The objective of this study was to investigate the immunophenotypic characteristics of T-cell acute lymphoblastic leukemia (T-ALL). Immunophenotyping was performed in 140 T-ALL patients by flow cytometry using a panel of monoclonal antibodies and CD45/SSC gating. The results showed that the T-lineage-associated antigen expressions were CD7 > CD2 > CD3 > CD5 successively. The positive rate of CD10 was 19.42% in patients. Among 140 cases of T-ALL, 12 (8.57%) was accompanied by B-lineage associated antigen expression. Myeloid antigen expression was identified in 31 out of 136 cases (22.79%). None of them expressed CD14 antigen. The positive rate of CD34 was 31.06%. The positive rate of myeloid antigen expression in CD34(+) T-ALL (36.58%) was significantly higher than that in CD34(-) T-ALL (15.38%) (p < 0.01). The expression of CD3 in child T-ALL was higher than that in adult T-ALL, whereas the expression of CD33 in children was lower than that in adults. It is concluded that immunophenotyping is an important tool for diagnosis of T-ALL. Immunophenotypic characteristics of T-ALL is heterogeneous.