The aim of the present study was to investigate the electrophysiological characteristics of the different layers of the olfactory bulb (OB). We used an in vitro OB slice coupled onto a microelectrode array (MEA) for simultaneous detection of spontaneous activities of OB neurons at different sites. Different frequency oscillations dominated the different layers of the OB slice, and the gamma frequency oscillations mainly appeared in the glomerular layer. The waves consisted of negative, positive, and bidirectional spikes, and were distributed at the different layers of the OB slice. Thus, combination of the OB slice with MEA is a useful technique for identifying signal oscillations by multi-site synchronous measurement, and will allow further studies on olfactory information coding and processing function. The aim of the present study was to investigate the electrophysiological characteristics of the different layers of the olfactory bulb (OB). We used an in vitro OB slice coupled onto a microelectrode array (MEA) for simultaneous detection of spontaneous activities of OB neurons at different sites. Different frequency oscillations dominated the different layers of the OB slice, and the gamma frequency oscillations first appeared in the glomerular layer. The waves consisted of negative, positive, and bidirectional spikes, and were distributed at the different layers of the OB slice. Thus, combination of the OB slice with MEA is a useful technique for identifying signal oscillations by multi-site synchronous measurement, and will allow further studies on olfactory information coding and processing function.