An open protection circuit (300) for a backlight module includes a PWM (350) with a control port (351) to disable the PWM. A switch (371) has a gate and a source connected to the control port. A plurality of first input circuits (330) includes first diodes (331), each of which has a first positive terminal connected to the gate and a negative terminal connected to ground. A plurality of second input circuits (340) include input resistors (341) connected to the control port. A plurality of detecting circuits (310, 380) are connected to the fluorescent lamps (311) and the first and second input circuits respectively. Each detecting circuit includes a sampling resistor (313) connected to one of the negative terminals of the first diodes, thereby the control port of the PWM is pulled low when either one of the fluorescent lamps are open-circuit.