A backlight module and an illumination device thereof. The illumination device of the backlight module comprises a light source and a lens, disposed over the light source with a predetermined gap therebetween. The lens comprises a bottom surface as an incident surface, a pair of upper refracting surfaces, and a pair of lateral refracting surfaces. The upper refracting surfaces form an included angle substantially in a range of about 80.degree. to about 120.degree..