A material compatible with blood obtained by heparinizing a polymer having quarternary ammonium groups with an alkali metal salt or an alkaline earth metal salt of heparin or the analog by ion exchange is provided. The equivalent ratio (M/S) of alkali metal atoms or alkaline earth metal atoms (M) in the heparin or the analog bonded to the polymer to sulfur atoms (S) in heparin or the analog bonded to the polymer is 0.4 or less.