The present invention discloses a side light type backlight module and a back plate heat dissipation structure thereof. The back plate heat dissipation structure comprises a bottom part, at least one side wall part and an extension part. The bottom part forms a main body of the back plate heat dissipation structure. The side wall part is formed by at least one edge of the bottom part extending upwards for at least one light source set attached on the inner surface thereof. The extension part is formed by the edge of the bottom part extending upwards. The heat generated by the light source set is conducted to the extension part and the bottom part through the top and the bottom of the side wall part. The total heat dissipation efficiency of the side light type backlight module can be raised by a dual way heat dissipation module.