Serotonergic neurons in the raphe nuclei are involved in a variety of brain functions by their extensive neural innervation, including depression, anxiety, sleep-wake cycles, reward, patience in decision making, and sexual preference. Serotonergic projections from the dorsal and median raphe nucleus densely innervate the olfactory bulb, where they can modulate the initial representation and processing of olfactory information. In recent years, with the application of electrophysiology, optical imaging and optogenetic techniques, numerous in vitro and in vivo studies have demonstrated the effects of serotonergic modulation from the raphe on the olfactory bulb and olfaction related behaviors, and revealed the underlying neural mechanisms. This article reviewed the most recent progresses about the modulatory effects of serotonergic projections from the raphe neuclei on defined cell types in the olfactory bulb.