Abstract： AIM:To investigate the location of p53 and the expression of active caspase-3 during the apoptosis of alveolar type Ⅱ epithelial cells(ATII cells)induced by oxidative stress. METHODS:ATII cells from adult Sprague-Dawley rats were separated,purified and cultured.500μmoL/L H_2O_2 was added into primary ATII cells for varlous times.The nuclei changes induced by H_2O_2 were observed under fluorescence microscope after DAPI staining.Apoptotic ratios and the expression of active caspase-3 were measured by flow cytometry and Western Blot analysis,respectively.The expression and location of p53 was detected by immunofluorescence and observed under laser confocal microscopy.RESULTS:Normal cell nuclei appeared large and emiting light blue fluorescence,while nuclei became small,condensed and often exhibitted a halo effect after H_2O_2,treatment observed under fluorescence microscope with DAPI staining.The cell apoptotie ratios and the expression of active caspase-3 were increased with the time of the H_2O_2 stimulation prolonged compared with the controls(P all<0.05).H_2_O2 treatment for 3 h increased p53 expression and the nuclei translocation of p53 was evident in the merged images under laser confocal microscopy.CONCLUSION:High level of oxidative stress injured cell nuclei,up-regulated the expression of active caspase-3 and the nuclei translocation of p53,and induced ATII ceHs apeptosis.p53 may mediate the apoptosis through transcription.