A biomedical signal sensing circuit including a first and a second modulation unit, an amplifying unit, a first and a second demodulation unit is provided. The first modulation unit performs a first modulation operation to a first biomedical signal according to a first signal to generate a first modulation signal. The second modulation unit performs a second modulation operation to a second biomedical signal according to a second signal to generate a second modulation signal. The amplifying unit amplifies the first and second modulation signals, and adds the amplified first and second modulation signals to generate a third modulation signal. The first demodulation unit performs a first demodulation operation to the third modulation signal according to the first signal to generate a first sensing signal. The second demodulation unit performs a second demodulation operation to the third modulation signal according to the second signal to generate a second sensing signal.