A catalyst composition for living free radical polymerization. The catalyst composition includes a transition metal complex MXp and a ligand, wherein M is a transition metal; X is halogen, —NO2, —NCS, —NCO, —SCN, —CN, —N3, —SO4, carboxylate group, or —PF6; p is the valence of the transition metal, the ligand is represented by formula (I): wherein R1 can be the same or different and is C1-20 alkyl, C6-20 aryl, C7-20 alkylaryl, C7-20 arylalkyl, or heterocyclic groups; R2 can be the same or different and is H, C1-20 alkyl, C6-20 aryl, C7-20 alkylaryl, C7-20 arylalkyl, heterocyclic groups, alkyl sulfide groups, nitrile groups, alkylsilyl, or ester groups; n is an integer of 0 to 6; and A is deleted or an S or O atom, wherein the molar ratio of the transition metal complex MXp and the ligand is 1 to 4. The catalyst composition of the present invention can be used to polymerize (meth)acrylic, vinyl, vinylidene, and diene monomers, and the polymer obtained has narrow polydispersity.