A method for preparing PRP conjugate with excellent storage stability and a process for preparing a Hib conjugate vaccine are provided. A method for preparing PRP conjugate of the present invention is characterized by that, in carrying out a binding reaction between PRP and a carrier protein, PRP with a lowered molecular weight than that of native PRP is used to suppress release of PRP from the PRP conjugate after preparation. A Hib conjugate vaccine comprising as an antigen the PRP conjugate obtained by the method has also excellent storage stability and retains sufficient immunogenicity.本發明提供保存安定性優良之PRP接合物的調製方法及Hib接合型疫苗之製造方法。本發明之PRP接合物之調製方法之特徵為當進行PRP與載體蛋白質之結合反應時，藉由使用比天然PRP更低分子化之PRP，抑制PRP從調製後之PRP接合物的游離。以由本調製方法所得到之PRP接合物作為抗原的Hib接合型疫苗，亦同樣地保存安定性優良，且保持充分之免疫原性。
