An optical touch module includes a screen and at least one optical positioning device disposed on the screen. The optical positioning device includes a case, at least one light emitting unit, a circuit board, a transparent diffusing part and an image capturing unit. The light emitting unit is disposed on case for emitting invisible light. The circuit board is electrically connected to the light emitting unit for controlling the light emitting unit. The transparent diffusing part is disposed at a light emitting side of the light emitting unit. A bar structure is formed on a light entrance surface of the transparent diffusing part for scattering the invisible light to be distributed over a touch surface of the screen. The image capturing unit is disposed on the case to capture an optical image for a touch object on the touch surface when the touch object is illuminated by the invisible light.