A method of controlling a brake lamp of a vehicle including an electric motor as a power source includes determining whether gear shifting is required and whether there is a forward section with a suddenly changing slope when regenerative braking is performed through the electric motor without manipulation of an accelerator pedal or a brake pedal, delaying the gear shifting until the gear shifting exceeds a gear-shifting limit when the gear shifting is required and when there is the forward section with the suddenly changing slope, calculating acceleration based on regenerative braking torque while the gear shifting is delayed, and controlling the brake lamp based on the calculated acceleration.