Objective To study the best protecting dosage of phycocyanin on PC12 cells after anoxia/re-oxygen in vitro.Methods The anoxia/re-oxygen cell models were established with cultured PC12 cells and treated by phycocyanin.The absorbency of PC12 cells was determined by MTT method to observe the activity and number of PC12 cells after anoxia/re-oxygen.The fluorescent intensity in PC12 cells labeled by Rhodamine123 was measured with laser scanning confocal microscope to observe the mitochondrial membrane potential after anoxia/re-oxygen.Results After anoxia/re-oxygen,the absorbency and fluorescent intensity in PC12 cells were significantly lower than those in control group.After treatment with phycocyanin,the absorbency of PC12 cell in test groups was higher than that in model group,especially in 5?g?mL-1 subgroup,P