The collisional reaction of droplets is observed by time-resolved fluorescence spectroscopy. Colliding droplets of the reactant solutions are irradiated with a pulsed laser, and the resulting fluorescence spectra and images of the colliding droplets are observed as a function of the elapsed time from the collision. The amidation reaction of dansyl chloride with isopropylamine is observed through fluorescence enhancement on a microsecond time scale. The present method enables us to measure the early stages of reactions in solutions.