Objective To study the survival and infiltration condition of cord blood derived-T lymphocytes in mice and its therapeutic action for erythroleukemic (EL) mice; and to provide the experimental and theoretical basis for studying the biological characteristics and antileukemia effects of cord bloodderived T cells. Methods Fourty-eight BALB/c mice were randomly divided into three groups, the control group(CG),the experimental group 1(EG 1)and the experimental group 2(EG 2). Cord blood derivedT lymphocytes were separated and prepared, and transplanted it into EL mice via the tail vein or peritoneal injection after being signed to their group. This was done in order to observe the survival time and infiltrate condition of the cord bloodderived T cells in mice and its effect on the morphosis of EL mice spleen by immunofluorescence (IMF), immunohistochemistry (IMC) and transmission electron microscope (TEM). Results Most activated cells were CD3SUP>+ /SUP>T lymphocytes by PHA, and the positive rate was (83.42±1.26)%; human CD3SUP>+/SUP> cells and BrduSUP>+/SUP> cells were detected in peripheral blood, spleens and liver of all mice at the 3rd and 7th day after cord blood derived-T lymphocytes were transplanting; CD25SUP>+/SUP> cells could be detected in the liver and spleen of EL mice in both experimental groups; and the average survival time of EL mice in the two experimental groups was (27.25±7.06) days and (24.74±2.93) days respectively (this was statistical significance compared to control group, P<0.05). The results of Hoechst 33258 staining showed: 1.Nuclear fluorescence was uniform in the control group and there were few apoptotic cells; 2. In the experimental group, some of the leukemia cells appeared to have morphological changes consistent with apoptosis; chromatin had a high degree of cohesion; dense concentration,or splited into massives, edge was smooth and clear; Under TEM, leukemic cells infiltrate was generally observed in the spleens of the control group mice. Parts of the leukemic cells showed typical apoptosis morphological changes in the experimental groups: nuclear chromatin concentration and edge accumulation was seen；nuclei fragmentation and formation of apoptotic bodies; the expansion of RER, and the vacuolar or medullar degeneration of mitochondria could be found. Conclusion The cord bloodderived T lymph