A backlight module detecting abnormal lamp tubes and an LCD employing such a backlight module are proposed. The LCD includes a voltage calculator for detecting voltage applied on ends of a lamp tube to monitor the lamp tube. Once the lamp tube becomes abnormal, the voltage varies accordingly. The voltage calculator calculates a voltage signal from a plurality of lamp tubes and produces a voltage value. A protection circuit regards the voltage value as a feedback signal to decide if there are any abnormalities. Once any of the lamp tubes is abnormal, the protection circuit transmits the voltage signal to a pulse-width modulated integrated circuit (PWM IC) to activate a protective function. The protection circuit of the present invention obtains the protection signal by sampling the voltage signal of the ends of the lamp tube and then gets the control signal by means of the calculation of the voltage calculator. Thus, voltage level retrieved from the protection signal are less easily affected by dimming and temperature.