Oxytocin is a peptide hormone known for its strong central actions regulating a variety of behaviors including parenthood and social bonding to others, in addition to the long-known peripheral actions. Despite increasing realization of its importance, dynamics and sites of action of oxytocin in the brain are poorly understood due to a lack of appropriate probe; it is too small to be tagged with bulky fluorophores for visualization. Therefore, to overcome the current technical limitation and to facilitate the understandings of oxytocin’s action in the brain, we tried to develop and apply a new probe. To this end, we conjugated oxytocin with “alkyne-tag” via a widely applicable simple coupling reaction. The alkyne-tag is far smaller than oxytocin, so it is expected that its tagging will be possible without significantly changing the original properties of oxytocin molecule. After incubation with the living brain tissues where alkyne-oxytocin behaves similarly to endogenous oxytocin, the tagged-oxytocin can be specifically visualized by a click chemistry reaction. Using this probe, we conducted various experiments to characterize the spatiotemporal dynamics of oxytocin in brain tissues. Here, I will introduce our novel strategy and findings brought by this probe including the region-specific binding sites and dynamics of oxytocin.