A portable electronic apparatus and a method for controlling a light source thereof are provided. The portable electronic apparatus comprises a main control module, a light control module, and a light source module which is configured to generate light. The method comprises the following steps: storing a plurality of light control parameters into the main control module; outputting one of the light control parameters to the light control module by the main control module in response to an input signal; and generating and transmitting a light control signal to the light source module through the light control module in response to the outputted light control parameters. As a result, the brightness of the light generated by the light source module is controlled.