Drebrin is an F-actin-binding protein which plays an important role in regulation of spine morphology and consists of two major isoforms, drebrin A and E. We have previously demonstrated that drebrin E, but not drebrin A is expressed in cell soma of newly generated neurons (Song et al., 2007). This suggests that drebrin E may have a critical role for generation, survival or differentiation of newly generated neurons. To better understand the role of drebrin E in the brain function, we generated drebrin knockout mice (DXKO). We immunohistochemically analyzed the number of mature and newly generated neurons in dentate gyrus of hippocampus (DG) and olfactory bulb (OB). In the DG of DXKO the number of NeuN-positive mature neurons and doublecortin-positive newly generated neurons were not changed. However, in the OB of DXKO the number of newly generated neurons was significantly decreased compared to those of wild-type mice (WT), whereas the number of mature neurons was not. Since in OB newly generated neurons are exchanged with existed neurons, we then examined newly generated neurons survival in OB. One day and 4 weeks after injection of BrdU, we counted the number of BrdU positive cells in OB. At 1 day after the injection, cell number of DXKO was small compared to WT. But at 4 weeks this difference was reversed. Next, we subjected adult male DXKO to behavioral tests to explore the functional role of drebrin. DXKO showed abnormal behavior in buried food test and three-chamber social interaction test which were OB related behavior but not in other fundamental behavioral tests. In Golgi stain we observed dendritic spines in DG and OB of DXKO, and this suggests that the olfaction disorder was not caused by deficit of spine genesis. The present behavior analysis indicates that DXKO show impairment of olfaction. And the immunohistochemical data indicate that the adult neurogenesis in DXKO is reduced but newly generated neuron survival was increased in OB. DXKO may show olfactory disorders because of the delayed exchange of newly generated neurons with existed neurons in the adult OB.