Multi-neuronal recording using calcium imaging usually relates calcium activity to electrical activity by assuming a dependency between them. Using calcium imaging and on-cell patch clamp recordings, we investigate calcium activities in mitral (MCs) and granule cells (GCs) in the olfactory bulb and characterize their relationship with the electrical activities. Bulbar neurons exhibit prominent on-going [Ca2+]i fluctuations that are observed in more cells and have higher frequency in the mitral cell layer than in the granule cell layer. Odorant stimulation elicits complex increasing or decreasing [Ca2+]i response waveforms in MCs, but the responses in GCs are stereotyped increasing responses. Simultaneous calcium imaging and electrical recording reveal a precise correlation between [Ca2+]i rises and occurrence of spikes in MCs. In contrast, GCs show much lower correlation between [Ca2+]i and spikes. In some cases, odor-evoked [Ca2+]i increases are much longer, and spikes are only partly correlated with the increases. In other cases, spikes in the decay phase of [Ca2+]i often occur alone without corresponding [Ca2+]i increases. The results indicate that calcium activities and their relationships with the electrical activity are different in MCs and GCs. Thus, one must think of the diversity of neurons when relating calcium activity to spike activity.