PROBLEM TO BE SOLVED: To provide a protein adsorption inhibitor which does not affect a measurement system using a biological specific reaction and to provide a protein adsorption inhibition method using the same.SOLUTION: A protein adsorption inhibitor includes a mixture of anionic system polymer (A) and cation system polymer (B). A mixing ratio of the polymer (A) and the polymer (B) is a mass ratio of 3:7-7:3. The inhibitor inhibits adsorption of a protein to a solid phase of a hydrophilic polystyrene base material in a measuring method using a biological specific reaction.