The present invention relates to a rubber modifier, a conjugated diene-based polymer including a functional group derived from the modifier, and a method for preparing a modified and conjugated diene-based polymer using the modifier. The modifier is used as the modifier of a conjugated diene-based polymer and combined with a conjugated diene-based polymer chain to easily introduce a functional group having affinity with a filler. Accordingly, a modified and conjugated diene-based polymer prepared using a compound of the rubber modifier may have excellent affinity with a filler, and as a result, molded articles (for example, tires) manufactured from a rubber composition including the polymer may have excellent tensile strength, abrasion resistance, and wet traction.