A series of polyacrylates with different n-alkyl side chain lengths (1 to 6, and 12 carbons) and a omega-methoxy terminal group (poly(omega-methoxyalkyl acrylate): PMCxA) were prepared to study their nonthrombogenicity using human platelet adhesion, micro bicinchoninic acid (micro BCA) protein assay, and enzyme-linked immunosorbent assay (ELISA) tests. In all cases, human platelet adhesion was suppressed on the PMCxA-coated substrates, and the number of human platelets adhered to thePMCxA(poly(3-methoxypropylacrylate))-coated surface was comparable to that of commercialized nonthrombogenic coating agent poly(2-methoxyethyl acrylate) (PMEA, equal to PMC2A). The amount of protein adsorbed onto the PMCxA was investigated by micro BCA using bovine serum albumin (BSA) and human fibrinogen (hFbn), revealing that PMC3A exhibited significantly high resistance to nonspecific BSA adsorption. Additionally, the amount of hFbn adsorbed onto the PMC3A was suppressed to the same extent as PMEA. The exposure degree of platelet adhesion sites in adsorbed hFbn was evaluated using an ELISA test, and the degree on the PMCxA with three to six methylene carbons was comparable to the PMEA. The hydration water structure in the hydrated PMCxA was also characterized using differential scanning calorimetry (DSC). The amount of intermediate water, which is the hydration water molecules that moderately interact with the polymer matrix, was maximum in the PMEA with two methylene run lengths, whereas the amount decreased by increasing the number of methyelnes in the side chain. The amount of adsorbed protein increased with a decrease in the amount of intermediate water, suggesting that the protein adsorption amount is tunable by simply changing the number of methylene carbons in the side chain. The present study revealed that poly(omega-methoxyalkyl acrylate)s are useful for blood-contacting medical devices, and PMC3A is the best mode of PMCxA to apply as an antiprotein adsorption coating agent.