Well-controlled poly(N-vinylpyrrolidone) (PVP)-grafted silicon surfaces were prepared by surface-initiated atom transfer radical polymerization (SI-ATRP) with 1,4-dioxane/water mixtures as solvents and CuCl/5,7,7,12,14,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane (Me6TATD) as a catalyst. The thickness of the PVP layer on the surface increased with reaction time, suggesting that the ATRP grafting of N-vinylpyrrolidone (NVP) from the silicon surfaces was a well-controlled process. The water contact angle and X-ray photoelectron spectroscopy (XPS) were used to characterize the modified surfaces. The protein adsorption property of the PVP-grafted surfaces was evaluated using a radiolabeling method. Compared with unmodified silicon surfaces, a Si-PVP60 surface with a PVP thickness of 15.06 nm reduced the level of adsorption of fibrinogen, human serum albumin (HSA), and lysozyme by 75, 93, and 81%, respectively. Moreover, the level of fibrinogen adsorption decreases gradually with an increase in PVP thickness. However, no significant difference in fibrinogen adsorption was found when the PVP layer was thicker than the critical thickness of 13.45 nm.