The present invention relates to a catalyst composition including a transition metal compound represented by the following Formula 1; and one or more of a compound represented by the following Formula 2, a compound represented by the following Formula 3 and a compound represented by the following Formula 4. The catalyst composition according to the present invention has excellent copolymerization properties, and can be usefully used as a catalyst for a polymerization reaction for preparing an olefin-based polymer having a high molecular weight.