A modified conjugated diene-based polymer, and more particularly, a modified conjugated diene-based polymer having a unimodal molecular weight distribution curve measured by gel permeation chromatography (GPC), molecular weight distribution (PDI; MWD) of less than 1.7, and a Si content of 100 ppm or more based on weight, and including a repeating unit derived from an aromatic vinyl monomer in an amount of greater than 0 wt % and less than 15 wt %, and a rubber composition including the same.