A transition metal compound represented by Chemical Formula 1 and a method for preparing the same, catalyst compositions including the same, and olefin-based polymers prepared from the same are disclosed herein. The transition metal catalyst has excellent structural stability together with excellent catalytic activity and can exhibit excellent copolymerizability even at a high temperature. In an embodiment, an olefin-based polymer prepared using a catalyst composition including the transition metal compound has a density of 0.91 g/cc or less.