There is provided a protein adsorption inhibitor comprising a compound represented by Formula (1) as an active ingredient. The protein adsorption inhibitor is capable of highly inhibiting non-specific adsorption of a protein such as an antibody or an enzyme to a surface of a base body such as an immune reaction vessel or an assay instrument. There is further provided a coating layer-formed base body having a coating layer containing the protein adsorption inhibitor on the base body. The coating layer-formed base body has an excellent protein adsorption-inhibiting function. There is still further provided a method for inhibiting the adsorption of the protein to the base body comprising forming the coating layer containing the protein adsorption inhibitor on the surface of the base body. In Formula (1), X is a hydrogen atom or a methyl group and n is an integer of 9 to 15.