Provided is a lighting device for an automobile air vent. The lighting device for an automobile air vent has a variable resistor, a light emitter, a light guide, and a diffusion plate. The variable resistor is connected to a knob of an air vent and is configured to vary resistance according to a manipulation amount of the knob. The light emitter is connected to the variable resistor and is configured to emit light such that brightness or color of the light is varied according to the variable resistance varied by the variable resistor. The light guide is configured to guide the light emitted by the light emitter. The diffusion plate is installed in an air vent housing of the air vent and is configured to diffuse the light guided through the light guide.