A signal readout circuit comprises a first amplifier, a second amplifier and first to fourth transistors. The signal readout circuit has a first electrode, a second electrode, and a third electrode. The signal readout circuit applied in a wide current-sensing range of amperometric chemical sensing. The readout circuit may be applied in electrochemical sensing such as glucose, so as to read out a current signal of an amperometric sensor. Through a design of low input impedance, sensing signals in a wide current range can be sensed in the readout circuit. Also, a current mirror structure is used to copy the input current to an output current, such that an output signal range of the output signals of the current circuit is not limited by a supplied voltage.