Accelerating the clearance of toxin in the brain extracellular space (ECS) has grown a promising strategy for treating some central nervous system diseases. As oldest sensory system, we know little about the influence of olfaction on the brain, but preclinical studies such as treatment of neurological diseases through it are in the ascendant. This makes it important to clarify the effects of olfaction on brain ECS and interstitial fluid (ISF) drainage. In this study, the effect of olfactory stimulation (eugenol, EUG) on ISF flow in hippocampus and its association with aquaporin 4 (Aqp4) had been investigated. The results show that eugenol can significantly increase the activity of hippocampal neurons, but reduce the clearance and diffusion rates of Gd-DTPA and A-594 in hippocampus. Similarly, eugenol inhalation slows down the rate of Gd-DTPA in CSF entering the hippocampus and its clearance. And knockout of Aqp4 gene aggravated these processes. In vitro results showed that after Aqp4 gene silencing, astrocytes grew slowly, with significantly decreased cells number, less nuclei, atrophied bodies and shorter processes. These results concluded that olfactory stimulation can change the ECS structure of the hippocampus, slow down the ISF drainage, and improve the function of neurons, while Aqp4 plays important roles. (C) 2019 Published by Elsevier Inc.