Immunoglobulin G (IgG) binds specific antigens, and IgG‐antigen complexes primarily activate immune cells and the complement system. These immune reactions are known to affect neural functions through the production and release of mediators such as cytokines. The high affinity IgG receptor FcγRI, but not the low affinity receptors FcγRII and FcγRIII, was expressed on the mouse dorsal root ganglion (DRG) neurons, especially small‐ or medium‐sized neurons. IgG bound to DRG neurons and made a complex with antigen there. Ragweed pollen bound to nerve fibers in the skin of sensitized mouse in situ. The formation of IgG‐ragweed pollen complex increased the concentration of Ca²⁺ ions in the DRG neurons. This increase was inhibited by a Ca²⁺ chelator, L‐ and N‐type voltage‐dependent Ca²⁺ channel blockers, and anti‐FcγRI antibody. IgG‐antigen complex released substance P from DRG neurons, which was inhibited by L‐ and N‐type Ca²⁺ channel blockers. Thus, IgG and antigen combine on primary sensory neurons to directly activate them, which may be a novel type of immune‐neuron linkage.