A modified conjugated diene-based polymer and a rubber composition including the same are disclosed herein. In some embodiments, the modified conjugated diene-based polymer includes a modified monomer-derived functional group represented by Formula 1, and an aminoalkoxysilane-based modifier-derived functional group at least one end thereof, wherein the polymer having a unimodal molecular weight distribution, and a polydispersity index (PDI) of 1.0 or more to less than 1.7. The polymer has a narrow and unimodal molecular weight distribution, and has excellent tensile properties and viscoelastic properties while having excellent processability.