Carbon dots are fluorescent carbon-based nanoparticles with great potential in bioimaging because they offer multiple imaging windows owing to their excitation-dependent emission features. A recent theoretical study shows that emission of graphene quantum dots responds to external electric field due to Stark effect. Inspired by this work, we have demonstrated here the first experimental study of the Stark effect of fluorescent carbon dots synthesized via a soft-template method. The carbon dots exhibit excitation-dependent emission covering blue to orange emission range. After being encapsulated in artificial lipid bilayers, the carbon dots show voltage-sensitivity of fluorescence. The fluorescence intensity change per mV is comparable with that of commercial membrane potential sensing dyes. Our results demonstrate the great potential of carbon dots in membrane voltage sensing.