A resistance-measuring circuit includes a controller for outputting a PWM signal and further for adjusting the duty cycle of the PWM signal, and a sampling circuit for processing the PWM signal and transmitting the processed PWM signal to the sensor. The sampling circuit samples the signal outputted from the sensor to generate a sampled signal with the voltage thereof changing according to any change in the duty cycle of the PWM signal, and further transmits the sampled signal to the controller. The controller obtains the real-time duty cycle of the PWM signal when the voltage of the sampled signal reaches a threshold voltage, and further calculates the exact resistance of the sensor according to the obtained real-time duty cycle of the PWM signal and the threshold voltage. An electronic device with the resistance-measuring circuit is also provided.