The olfactory bulb (OB), an important odor information processing center in olfactory system, not only has heavy intermutual neural projections with brain areas related to olfaction, including piriform cortex, amygdala, hippocampus and striatum, but also receives regulatory affections from other brain regions such as raphe nuclei and locus eoeruleus.All of these projections provide the possible modulation of the activity in the OB by brain states.The awake and anesthetized states are two different brain conditions and are both used extensively in electrophysiological studies of OB.However, the activity patterns of OB local field potentials (LFP) in responding to odor stimulation at different brain states are unclear.To clarify this question, the LFP oscillations at granule cell layer of the OB in awake and anesthetized animals were recorded.We found that the LFP responses induced by odor in awake state were complex, with different frequency bands showed different patterns: 13-30 Hz, increased significantly; 30-60 Hz, almost no response; and 60-90 Hz, decreased significantly.In addition, the increased response of 13-30 Hz was transient, whereas the decreased response of 60-90 Hz was long-lasting.However, when the animals were anesthetized by chloral hydrate, all of the three frequency bands showed significantly increased and long-lasting responses.Therefore, the activity patterns of OB LFP in responding to odor stimulation are significantly different when the animals are under awake and anesthetized states, reflecting different neural mechanisms involved in the odor information processing under the two brain states.