A sheetless backlight module and a light guide plate thereof are provided. The light guide plate includes a body and a plurality of light scattering units. The body has a bottom and a plurality of microstructures formed on the bottom and recessed in the body from the bottom. The pluralities of light scattering units are disposed in a plurality of spaces formed due to the plurality of microstructures recessed in the body. A manufacturing method of the light guide plate mentioned above includes forming the plurality of microstructures on the bottom of the body; preparing a fluid solution containing at least a diffusive reflective material; distributing the fluid solution on the bottom; driving the fluid solution to flow into the microstructures; removing the part of the fluid solution outside the microstructures; and solidifying the fluid solution to form the plurality of light scattering units.