Objective To study cell morphological change of glucocorticoid(GC)induced murine thymocyte death. Method After intraperitoneal injection of dexamethasone into 4-6-week-old female BALB/C mice, terminal deoxynucleotidyl transferase (TdT)-mediated dUTP-biotin nick end-labeling (TUNEL) method was used to detect the DNA fragmentation or double strand breaks. To examine acid phosphatase (ACP), we applied double staining of the section with the TUNEL method and ACP. Moreover, we used transmission electron microscopy to observe ultrastructure of apoptosis cells and macrophages as well as the activity of macrophages after apoptosis. Results We demonstrated under light microscopy that, the TUNEL positive thymocytes were scattered throughout the cortex of GC-treated thymus, and the apoptosis index was 0.460±0.012;In the control group, the TUNEL positive ones were few and the apoptosis index was 0.020±0.001. There was significant difference between the two groups(EM>P/EM><0.05). Double staining revealed that all the TUNEL positive cells were phagocytosed by ACP positive macrophages. It was also observed by transmission electron microscopy, and these small unphagocytosed thymocytes were apparently dead cells, as based on the extent of chromatin condensation was enormous. Conclusion Typical apoptosis, which is characterized by DNA fragmentation, was not the dominant type of GC-induced murine thymocyte death. These dead thymocytes were phagocytosed by ACP positive cells.The most important effect of GC for thymocyte was that it can induce chromatin pycnosis without DNA fra