In this paper, we propose a method for monitoring the motion of cows by tracking the white patterns on them with constrained deformable models. As input for observation, we use image sequences of overhead views of cows taken by a camera installed on the ceiling of a breeding room. First, the 3D coordinates of the boundaries of the white patterns on the head, neck and torso parts respectively are registered. For each body part, the relationship between variations of the patterns in appearance and the parameters specifying the movement are defined in advance from that part?s movement characteristics. Using deformable models which are constrained to be deformed based on these relations, the boundaries of the patterns are robustly tracked, producing as output the parameters specifying the movement of each part. Preliminary experiments using actual image sequences have shown the practical usefulness of the proposed method.