The conjugated diene polymer is a conjugated diene polymer produced using the catalyst composition f

The present invention provides a catalyst composition including a functionalizing agent of the following Formula 1 together with a rare earth metal compound, an alkylating agent, and a halogen compound, having good catalytic activity and polymerization reactivity and useful for the preparation of a conjugated diene-based polymer having high linearity and excellent processability, and a conjugated diene-based polymer prepared using the catalyst composition. €ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ€ƒ[Formula 1]€ƒ€ƒ€ƒ€ƒ€ƒ(X 1 ) a -Sn-(X 2 ) 4-a In Formula 1, a, X 1 , and X 2 are the same as defined in the disclosure.