Objective. To design a new type of circuit for measuring frequency & duty cycle of stimulated bioelectrical signal for the project of "the map of neuron-threshold in human brain and its clinical application". Method. This circuit was designed according to the character of stimulated bioelectrical signals. It was tested and improved and then used in the neuron-threshold stimulator. Result. The circuit was found to be very accurate for measuring frequency and the error for measuring duty cycle was below 0.2%. Conclusion. This circuit is well-designed, simple, easy to use, and can be applied in many systems.