We present a new boundary extraction model, called the quantum contour model. First, we discuss the well known and widely used deformable models from a point of view of classic mechanics. Then, boundary extraction is further considered as the motion of a particle described by quantum mechanics, which is in contrast to determining the minimum kernel energy associated with the boundary in an energy field of the deformable model. The principle and approach of boundary extraction based on particle motion in quantum mechanics are developed by estimating the probability that a particle moves from one point to another iteratively. Finally, experiments with simulated and real images demonstrate that the quantum-contour-based approach could extract a close boundary quickly, accurately, and robustly, with a single initial point close to the boundary of the object of interest.