An “active” and self-switchable nanoreactor is reported. This nanoreactor was made of nickel nanoparticles and a unique polymer composite of poly(1-vinylimidazole) (PVIm) and poly(acrylic acid) (PAAc) that exhibited “self-healing” properties. This nanoreactor revealed a weak reactivity at relatively low temperatures due to the complementary interaction between the PVIm and PAAc, which inhibited access to the catalytic sites of the nickel. In contrast, the nanoreactor demonstrated significant reactivity at relatively high temperatures, resulting from the dissociation of the interpolymer interaction. Unlike conventional nanoreactors, which usually involve the thermal phase transition of PNIPAm, this novel nanoreactor has employed the “self-healing” properties of supramolecular building blocks. The proposed incorporation of “active” supports to metal nanoparticles creates a new protocol for developing catalytic nanoreactors.