The present embodiment provides a driver's drowsiness warning system. The driver's drowsiness warning system according to the present embodiments of the present disclosure may include: a steering angle sensor that measures a steering signal; a lane recognizing sensor that recognizes a lane; a lane keeping assist unit that determines whether a vehicle is out of a lane that the vehicle drives along; and a controller that determines whether a driver is drowsy based on at least one out of a frequency of a change in the steering signal during a predetermined period of time and how frequently the vehicle is out of the lane during a predetermined period of time, and generates a warning to the driver when it is determined that the driver is drowsy.
System for warning of drowsiness of driver and method thereof