The olfactory bulb (OB) is one of the two major loci in the mammalian brain where newborn neurons are constantly integrated into the neural circuit during postnatal life. Newborn neurons are generated from neural stem cells in the subventricular zone (SVZ) of the lateral ventricle and migrate to the OB through the rostral migratory stream. The majority of these newborn neurons differentiate into inhibitory interneurons, such as granule cells and periglomerular cells. It has been reported that prolonged supply of newborn neurons leads to continuous addition/turnover of the interneuronal populations and contributes to functional integrity of the OB circuit. However, it is not still clear how and to what extent postnatal-born neurons contribute to OB neural circuit formation, and the functional role of postnatal neurogenesis in odor-related behaviors remains elusive. To address this question, here by using genetic strategies, we first determined the unique integration mode of newly born interneurons during postnatal development of the mouse OB. We then manipulated these interneuron populations and found that continuous postnatal neurogenesis in the SVZ-OB plays pivotal roles in flexible olfactory associative learning and memory.