A lamp driving method and an inverter for driving the lamp are disclosed which can stably maintain a desired duty ratio of a pulse width modulation (PWM) signal for controlling driving of a lamp. The method for driving lamp, comprising: generating an inner pulse width modulation (PWM) signal;outputting a DC level in response to a duty ratio of an external PWM signal; selectively outputting the external PWM signal or the inner PWM signal in accordance with the DC level; and generating an AC drive signal Acs in response to the external PWM signal or the inner PWM signal, and supplying the AC drive signal to the lamp.