A lens module has a module body and a mating receptacle. The module body has a lens unit and an image sensing and processing unit, the image sensing and processing unit receiving light beams from the lens unit and producing an image signal. The mating receptacle is made of insulating material, which is detachably engaged with the module body and has conductive terminals formed therein for transmitting the image signal. An assembling method of the lens module includes the following steps. First, the mating receptacle is installed on a printed circuit board of an electronic device by a surface mounting technology. Second, the module body is installed in the mating receptacle to implement electrical interconnection between the module body and the printed circuit board.