A modified conjugated diene-based polymer and a rubber composition including the same are disclosed herein. In some embodiments, a modified conjugated diene-based polymer includes a 1,2-vinyl bond content of 30.0 wt % or less with respect to a total weight of the modified conjugated diene-based polymer, wherein the polymer has a glass transition temperature of −90° C. to −50° C., a mooney viscosity of 50 to 100 measured by ASTM D1646, polydispersity index (PDI) of 1.5 to 3.5, and a mooney relaxation ratio of 0.7 or less when measured at 110° C.