An LED device with built-in fast self-test circuit includes at least one LED unit, a data shift and latch register, a control unit, at least one multiplexer, and an LED driver unit. The data shift and latch register receives a serial data signal. The control unit receives the serial data signal to detect whether there is normal data transmission based on the serial data signal. When there is no data transmission, the control unit enables a multiplex control signal. The multiplexer is connected to the control unit and the data shift and latch register. According to the multiplex control signal, the multiplexer selects the control unit or the data shift and latch register as an output. The LED driver unit is connected to at least one LED unit and the multiplexer to drive the LED unit based on the output of the multiplexer.