Rosemary oil (ROO) is known to have multiple pharmacological effects: it is an antioxidant, an antiin ammatory, and cytoprotective. In the present study, we examined the effects of ROO on Human olfactory bulb neuronal stem cells (hOBNSCs) after their transplantation into rats, with the ibotenic (IBO) acid-induced cognitive de cit model. After 7 weeks, cognitive functions were assessed using the Morris water maze (MWM). After two months blood and the hippocampus were collected for biochemical, gene expression, and histomorphometric analyses. Learning ability and memory function were signi cantly enhanced after hOBNSCs transplantation and were nearly returned to normal in the treated group. The IBO acid injection was associated with a signi cant decline of total leukocyte count (TLC) and a signi cant increase in total and toxic neutrophils. As well, the level of IL-1β, TNF-α CRP in serum and levels of MDA and NO in hippocampus tissue were signi cantly elevated, while antioxidant markers (CAT, GSH, and SOD) were reduced in treated tissue compared to controls. The administration of ROO before or with cell transplantation attenuated all these parameters. In particular, the level of NO nearly returned to normal when rosemary was administrated before cell transplantation. Gene expression analysis revealed the potential protective effect of ROO and hOBNSCs via down-expression of R-βAmyl and R-CAS 3 and R-GFAP genes.