Insoluble polystyrenes substituted with sulphonate and L-arginyl methyl ester (PAOM) present substituents mimicking the reactive binding site of antithrombin III. These materials have a specific affinity for thrombin. The binding of the enzyme is reversible and the eluted thrombin remains active. Consequently, these resins can be used as stationary phases in affinity liquid chromatography in order to purify thrombin with a high biological activity. The influence of different characteristics of such polymers (substitution ratio, average particle size, affinity constant, synthesis conditions) on the purification performance is studied. Human prothrombin complex concentrate is activated and applied onto the gel. A purified human thrombin of high specific activity is separated with a high recovery of biological activity of the enzyme.