A brake warning apparatus for bicycles is provided, including a lighting device and a switch handle, to be installed on the handles of bicycles. The lighting device includes a light case, a lighting unit and a power unit. The light unit includes at least a switch. The switch handle is partially coupled to the inside of the light case and the rod of the switch handle extending outside the light case is located on the path of the movement of the handbrake of the bicycle when braking the bicycle. When the switch handle is pressed by the handbrake, the rod inside the light case will trigger the switch of the lighting unit so that the lighting device will display the pre-defined lighting condition to achieve the warning effect.