A modified conjugated diene-based polymer, having a unimodal shape molecular weight distribution curve by gel permeation chromatography, and a molecular weight distribution (PDI; MWD) of 1.0 to less than 1.7, and comprising a functional group derived from a modification initiator represented by the following Formula 1 at one terminal and a functional group derived from a modifier represented by the following Formula 2 or Formula 3 at the other terminal, in Formula 1, M is an alkali metal, R 1 and R 2 are each independently hydrogen; an alkyl group of 1 to 30 carbon atoms; a heteroalkyl group of 1 to 30 carbon atoms comprising a N, O or S atom; a cycloalkyl group of 5 to 30 carbon atoms; an aryl group of 6 to 30 carbon atoms; or a heterocyclic group of 3 to 30 carbon atoms comprising one or more among N, O and S atoms; or R 1 and R 2 are connected with each other to form a cycloalkyl group of 4 to 20 carbon atoms; or a heterocyclic group of 3 to 20 carbon atoms comprising one or more among N, O and S atoms, R 3 is a substituted or unsubstituted alkylene group of 1 to 20 carbon atoms with an alkyl group of 1 to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbon atoms or an aryl group of 6 to 20 carbon atoms, a cycloalkylene group of 5 to 20 carbon atoms, or an arylene group of 4 to 20 carbon atoms, and R 4 is hydrogen; an alkyl group of 1 to 30 carbon atoms; a heteroalkyl group of 1 to 30 carbon atoms comprising a N, O or S atom; a cycloalkyl group of 5 to 30 carbon atoms; an aryl group of 6 to 30 carbon atoms; or a heterocyclic group of 3 to 30 carbon atoms comprising one or more among N, O and S atoms, in Formula 2, R 20 and R 23 are each independently a single bond, or an alkylene group of 1 to 10 carbon atoms, R 21 and R 22 are each independently an alkyl group of 1 to 10 carbon atoms, R 24 is hydrogen, an alkyl group of 1 to 10 carbon atoms, or a substituted divalent, trivalent or tetravalent alkylsilyl group with an alkyl group of 1 to 10 carbon atoms, a is an integer of 1 to 3, c is an integer of 1 to 3, and b is an integer of 0 to 2, where b+c = 3, in Formula 3, A 1 and A 2 are each independently an alkylene group of 1 to 20 carbon atoms, R 25 to R 28 are each independently an alkyl group of 1 to 20 carbon atoms, and L 1 to L 4 are each independently a substituted divalent, trivalent or tetravalent alkylsilyl group with an alkyl group of 1 to 10 carbon atoms, or an alkyl group of 1 to 20 carbon atoms. M is an alkali metal, R 1 and R 2 are each independently hydrogen; an alkyl group of 1 to 30 carbon atoms; a heteroalkyl group of 1 to 30 carbon atoms comprising a N, O or S atom; a cycloalkyl group of 5 to 30 carbon atoms; an aryl group of 6 to 30 carbon atoms; or a heterocyclic group of 3 to 30 carbon atoms comprising one or more among N, O and S atoms; or R 1 and R 2 are connected with each other to form a cycloalkyl group of 4 to 20 carbon atoms; or a heterocyclic group of 3 to 20 carbon atoms comprising one or more among N, O and S atoms, R 3 is a substituted or unsubstituted alkylene group of 1 to 20 carbon atoms with an alkyl group of 1 to 10 carbon atoms, a cycloalkyl group of 5 to 10 carbon atoms or an aryl group of 6 to 20 carbon atoms, a cycloalkylene group of 5 to 20 carbon atoms, or an arylene group of 4 to 20 carbon atoms, and R 4 is hydrogen; an alkyl group of 1 to 30 carbon atoms; a heteroalkyl group of 1 to 30 carbon atoms comprising a N, O or S atom; a cycloalkyl group of 5 to 30 carbon atoms; an aryl group of 6 to 30 carbon atoms; or a heterocyclic group of 3 to 30 carbon atoms comprising one or more among N, O and S atoms, R 20 and R 23 are each independently a single bond, or an alkylene group of 1 to 10 carbon atoms, R 21 and R 22 are each independently an alkyl group of 1 to 10 carbon atoms, R 24 is hydrogen, an alkyl group of 1 to 10 carbon atoms, or a substituted divalent, trivalent or tetravalent alkylsilyl group with an alkyl group of 1 to 10 carbon atoms, a is an integer of 1 to 3, c is an integer of 1 to 3, and b is an integer of 0 to 2, where b+c = 3, A 1 and A 2 are each independently an alkylene group of 1 to 20 carbon atoms, R 25 to R 28 are each independently an alkyl group of 1 to 20 carbon atoms, and L 1 to L 4 are each independently a substituted divalent, trivalent or tetravalent alkylsilyl group with an alkyl group of 1 to 10 carbon atoms, or an alkyl group of 1 to 20 carbon atoms.