Division of a millimeter-sized and compartmentalized fatty acid droplet is triggered by a chemical pH clock reaction operating on the ten-second time scale. The autonomous pH change inside the compartment translates into the deprotonation of the fatty acid molecules, leading to a negative interfacial tension at the water–oil interface inside the droplet. This phenomenon induces the expansion of the droplet, which is followed by its division into daughter droplets governed by the Plateau–Rayleigh instability.