Provided is a molecular imprint polymer that is capable of acquiring stealth properties through a new mechanism. The molecular imprint polymer according to the present invention, which has a plasma protein recognition sites molecularly imprinted by a plasma protein thereon and contains a constituent derived from a biocompatible monomer, is an in vivo stealth nanoparticle to be used in intravascular delivery. As the plasma protein, albumin is preferred. When carrying a drug thereon, the in vivo stealth nanoparticle according to the present invention is usable as a drug for drug delivery system.