A flat fluorescent lamp has a uniform screen brightness even with a low discharge initiating voltage. A backlight unit using the flat fluorescent lamp is provided. The flat fluorescent lamp includes a front substrate, a back substrate having a continuous serpentine type discharge channel defined by a plurality of partitions extending alternately from both side ends of the back substrate. An inverter and a pair of electrodes provided on one of the front and the back substrates apply power to the electrodes. Each of the electrodes includes discharge electrodes mounted in strip configurations and a plurality of subsidiary electrodes that are mounted to extend perpendicularly from the discharge electrodes and to correspond to positions of the partitions. The plurality of subsidiary electrodes are alternately connected to inner edges of both the discharge electrodes so that neighboring subsidiary electrodes have different polarities.