Objective To study the changes in activity of NADPH oxidase, the effects of signal molecules on membrane potential and ROS production of mitochondria in apoptotic murine peritoneal macrophages. Methods Laser scanning confocal microscopy, flow cytometry and fluorescence labeling were used. Results 1 The macrophages treated with dexamethasone developed apoptosis quickly and presented concomitant apoptotic changes. 2 Mitochondria membrane depolarized quickly, the activity of NADPH oxidase declined sharply, and ROS production decreased rapidly. The erasers of ROS promoted macrophage apoptosis. 3 PKC favored, and cAMP inhibited the macrophage apoptosis and the rapid drop in ROS and mitochondrial membrane depolarization. cGMP and TPK which slightly inhibited macrophage apoptosis, had no effects on ROS. Conclusion 1 The activity of NADPH oxidase declined sharply, hence the ROS decreased rapidly, which promoted apoptosis in macrophages treated with dexamethasone. 2 The signal molecules affected apoptosis by modulating ROS decline and mitochondria depolarization. The results suggested that, mitochondria variations, especially the variations of ROS and membrane potential, mainly affected macrophage apoptosis.;