A scan cell circuit for use in an integrated circuit chip is disclosed. The scan cell circuit includes a multiplexer receiving a first signal, a second signal and a selection signal, and outputting one of the first signal and the second signal in response to the selection signal, and a host circuit electrically connected to the multiplexer, receiving and processing an output of the multiplexer, and proceeding an optional output from a first output end and/or a second output end. When the multiplexer selects the second signal to be outputted in response to a specific state of the selection signal, the first signal output end is fixed at a constant level according to the specific state of the selection signal.