We analyzed the cellular composition of the juxtaglomerular region in the main olfactory bulb of C57B/6J strain mice, focusing on 1) the compartmental organization of the glomerulus and the presence of type 1 and 2 periglomerular cells, 2) the colocalization relationships among the 4 major chemically identified groups of periglomerular cells, glutamic acid decarboxylase (GAD)/gamma-aminobutyric acid (GABA), tyrosine hydroxylase, calretinin and calbindin D28k positive periglomerular cells, and 3) the chemical properties of the nitric oxide synthase (NOS)-positive juxtaglomerular cells. We confirmed the compartmental organization of the glomerulus and the presence of both type 1 and 2 periglomerular cells in the mice. Similar to rat periglomerular cells, the tyrosine hydroxylase-positive cells were type 1 and GAD/GABA-positive. On the other hand, both the calbindin D28k-positive and calretinin-positive cells were type 2 periglomerular cells, but in contrast to those in rats, which are GAD/GABA-negative, all of the calbindin D28k-positive periglomerular cells and 65% of the calretinin-positive periglomerular cells were GAD/GABA-positive. The GAD/GABA-positive cells thus included both type 1 and type 2 periglomerular cells. Juxtaglomerular NOS-positive cells have been proposed as a subgroup of type 1 periglomerular cells that are separate from the calretinin-positive and calbindin D28k-positive cells in rats. However, in the mice, about 70% of the NOS-positive cells were calretinin-positive, and 50% of the calretinin-positive cells were NOS-positive. We herein reveal the significant species differences in the chemical properties of periglomerular cells and suggest that the cellular organization of the mouse main olfactory bulb cannot be extrapolated from that of rats.