PROBLEM TO BE SOLVED: To provide a purification method of a plasma protein usable as an active ingredient of pharmaceuticals.SOLUTION: The invention relates to an affinity substrate which is used for selectively binding a plasma protein, and contains a solid substrate material on which a deoxyribonucleic acid aptamer is specifically fixed to the above plasma protein. The invention also relates to a purification method of the plasma protein comprising the following steps (a)-(c): (a) contacting the affinity substrate with a sample containing the plasma protein to form a complex between (i) a nucleic acid aptamer fixed on the affinity substrate and (ii) the plasma protein； (b) making the protein free from the complex formed in the step (a)； and (c) recovering the plasma protein in a purified form. The invention also relates to a pharmaceutical composition containing a purified composition of a recombinant human plasma protein.SELECTED DRAWING: None【課題】医薬品の活性成分として使用可能な血漿タンパク精製方法の提供。【解決手段】血漿タンパクを選択的に結合させるための親和性基質であって、固体の基質材料を含み、この固体の基質材料上で上記血漿タンパクにデオキシリボ核酸アプタマが特異的に固定されている親和性基質。下記の（ａ）～（ｃ）の工程を有する血漿タンパクの精製方法：（ａ）前記親和性基質と血漿タンパクを含むサンプルとを接触させて、（ｉ）前記親和性基質上に固定された核酸アプタと（ｉｉ）血漿タンパクマとの間に錯体を形成し、（ｂ）段階（ａ）で形成された錯体からタンパクをフリーにし、（ｃ）血漿タンパクを精製された形で回収する血漿タンパクの精製方法。組換え型ヒト血漿タンパクの精製された組成物を含む医薬組成物。【選択図】なし
