The free falling motions of thin circular disks in still water were investigated experimentally. All six degrees of freedom of a falling disk were determined by a stereoscopic vision method. For the disk of small dimensionless moment of inertia (I* < 6.0 × 10-3), three types of motions were identified, including a planar zigzag one and two newly discoveried motions. The two new motion both have non-planar trajectory and continous rotation
about the disk's symmetry axis. Flow visualizations were also carried out to show the wake structures with different types of motions.