Provided are a modified conjugated diene-based polymer comprising a conjugated diene-based monomer-derived repeating unit; and a chain extender-derived part which is linked to both terminals of the conjugated diene based monomer-derived repeating unit, respectively, includes one or more urethane groups in a molecular chain, and has different functional groups at both terminals, wherein one of the functional groups is an alkyne group, wherein a terminal of the chain extender-derived part which is not linked to both terminals of the conjugated diene based monomer-derived repeating unit is an alkyne group, a manufacturing method thereof, a binder composition for a solid propellant comprising the same, a modified conjugated diene based binder for a solid propellant, and a manufacturing method thereof.