An LED lighting system includes a luminescent unit driven by a rectified AC voltage and a bleeder circuit. The bleeder circuit includes a current source, a dimming detection unit and an adjusting unit. The current source is configured to provide a bleeder current according to a control signal. The dimming detection unit is configured to monitor the rectified AC voltage, thereby outputting a dimming detection signal associated with an operational mode of the LED lighting system. The adjusting unit is configured to output the control signal according to the dimming detection signal so as to instruct the current source to keep the bleeder current at a first value during a first period and at a second value smaller than the first value during a second period subsequent to the first period when the dimming detection signal indicates that the LED lighting system is operating in a dimming mode.