In the multicellular system, a variety of signaling molecules are supposed to mediate cell-to-cell communication. However, the information on their spatio-temporal dynamics remains largely elusive, likely due to the lack of the suitable technology. Since fluorescence imaging is a powerful approach to monitor the dynamics of signaling molecules, I decided to develop fluorescent sensors for various signaling molecules.　First, I developed a green fluorescent sensor for oxytocin, a neuropeptide that play critical roles in social behaviors, food intake, and stress responses. Through the screening of hundreds of mutants, I finally obtained a sensitive fluorescent sensor that show a large fluorescence change (up to 700% dF/F0). I applied this sensor to in vivo fiber photometry measurement, and found the active oxytocin dynamics in the brain upon a various physiological stimuli. Furthermore, I tried to extend the repertoire of the target signaling molecule of fluorescent sensors by using a similar way to the development of the oxytocin sensor. Through the screening, I succeeded in obtaining sensitive green fluorescent sensor for ~20 signaling molecules including chemical transmitters, peptide ligands, and lipid mediators. These fluorescent sensors will further extend our knowledge on the intercellular signaling dynamics in living systems.