An optical touch apparatus and a width detecting method thereof are provided. The optical touch apparatus includes at least two sensing components, a light emitting component, and a width detecting module. The sensing components are configured to sense a touch object located on a touch plane. The light emitting component is configured to be a light source of the touch plane and is disposed adjacent to one of the sensing components. The width detecting module is coupled to the light emitting component and the other of the sensing components. The light emitting component is controlled by the width detecting module to emit a light. The other of the sensing components is controlled by the width detecting module to sense intensity of the light. The width detecting module detects a distance between the sensing components according to the sensed intensity of the light.