Objective To study the effects of Panax Notoginseng Saponins (PNS) on the damaged expression of ZO-1 of brain microvascular endothelial cells caused by Aβ42.MethodsBrain microvascular endothelial cells were divided into normal control group, model group, PNS low-, medium- and high concentration groups. They were incubated for 24h in 5% CO2 incubator at 37℃ . Then cell vitality was detected by MTT colorimetric method and ZO-1 protein expression was tested by Western blot.Results Stimulation of Aβ42 reduced the activity of microvascular endothelial cells (P<0.01) and suppressed the expression of ZO-1 protein (P<0.01). Compared with the model group, the activity of microvascular endothelial cells of PNS groups, especially the high and medium dose groups (P<0.05), and increased the ZO-1 protein expression. Conclusion PNS can partly recover the barrier function of blood brain barrier through inhibiting the decrease of the activity of microvascular endothelial cells caused by Aβ42.