A bipolar junction transistor (BJT) pixel circuit, an image sensor and a driving method thereof are provided. The BJT pixel circuit includes a BJT, a photodetector, a feedback amplifier circuit, a shutter circuit, and a current generating unit. The photodetector generates a first base current to a base of the BJT responsive to a light incident on the photodetector. The feedback amplifier circuit is operative to increase an emitter voltage of the BJT according to the light intensity. The shutter circuit controls an exposure time of the photodetector according to a shutter signal. The current generating unit generates the second pulsed base current responsive to a trigger signal causing a base voltage of the BJT to drop while the feedback amplifier circuit operates to increase the emitter voltage of the BJT so as to build-up the base-emitter voltage to a predetermined voltage level when a light source turns on.