By transmission electron microscopy, DNA agarose gel electrophoresis, flow cytometry and TUNEL staining, changes of the murine peritoneal macrophages treated with high dose of dexamethasone were observed. The results clearly showed that, treated with high dose of dexamethasone, the macrophages presented various changes in ultrastructure: chromatin condensed and abutted sharply against the nuclear membrane, and cytoplasm condensed. Half hour after dexamethasone treatment, DNA ladder was visualized by agarose gel electrophoresis. The macrophages displayed TUNEL positive. The characteristic apoptosis peak of DNA was showed by flow cytometry. The results indicated that the macrophages treated with high dose of dexamesathone may develop apoptosis rapidly and efficiently.