目的：观察胸腺细胞凋亡的超微结构及其与ＤＮＡ裂解的相互关系。方法：对大鼠进行腹腔内糖皮质激素注射，对胸腺进行光、电镜观察，并作ＴｄＴ介导的ｄＵＴＰ缺口末端标记（ＴｄＴ－ｍｅｄｉａｔｅｄ－ｄＵＴＰｎｉｃｋｅｎｄｌａｂｅｌｉｎｇ，ＴＵＮＥＬ）。结果：皮质胸腺细胞出现凋亡的超微结构改变，少数细胞出现管网状结构。ＴＵＮＥＬ可标记不同阶段的凋亡细胞。结论：糖皮质激素可引起胸腺皮质细胞凋亡，上皮性网状细胞对凋亡细胞具有活跃的吞噬和降解作用。ＴＵＮＥＬ可选择性标记石蜡切片中的凋亡细胞，但对凋亡的判定需结合形态特点并与坏死鉴别 Objective: To observe the ultrastructure of thymocyte apoptosis and its relationship with DNA cleavage. Methods: Rats were injected intraperitoneally with glucocorticoid. The thymus was observed by light and electron microscope and TdT-mediated dUTP nick end labeling (TUNEL) was performed. Results: The ultrastructural changes of apoptosis in cortical thymocytes were observed. A few cells appeared tubular network structure. TUNEL can mark different stages of apoptotic cells. Conclusion: Glucocorticoid can induce apoptosis of thymus cortical cells, and epithelial reticular cells have active phagocytosis and degradation of apoptotic cells. TUNEL can be used to selectively label apoptotic cells in paraffin sections, but the determination of apoptosis needs to be combined with morphological characteristics and identified with necrosis