Cellulose thin films were chemically modified by in situ sulfation to produce surfaces with anticoagulant characteristics. Two celluloses differing in their degree of polymerization (DP): CEL I (DP 215-240) and CEL II (DP 1300-1400) were tethered to maleic anhydride copolymer (MA) layers and subsequently exposed to SO3 center dot NMe3 solutions at elevated temperature. The impact of the resulting sulfation on the physicochemical properties of the cellulose films was investigated with respect to film thickness, atomic composition, wettability and roughness. The sulfation was optimized to gain a maximal surface concentration of sulfate groups. The scavenging of antithrombin (AT) by the surfaces was determined to conclude on their potential anticoagulant properties.