Disclosed are a functional reinforcing filler including inorganic particles surface-modified with an alkenylsilanol obtained by hydrolyzing an alkenylalkoxysilane compound, and a method for preparing the same. Since the disclosed functional reinforcing filler has a functional group having a double bond, it has good reactivity for styrene-butadiene rubber and sulfur. Thus, when used as a functional reinforcing filler in the manufacture of rubber, it allows improvement of physical properties through adjustment of the addition amount of sulfur without additional use of the coupling agent. In addition, because of superior hydrolysis reactivity, the problem of alcohol can be solved and a rubber mixture with long scorch time can be prepared. In particular, when the functional reinforcing filler of the present invention is used in the manufacture of tires, improvement in modulus, tensile strength, rotational resistance and wet traction performance can be expected.