This blood cell agglutinating fiber contains a blood cell agglutinating agent inside thereof. It is preferable that: the penetration rate of the blood cell agglutinating agent into the fiber is at least 2； the fiber, preferably the freeness thereof being not more than 780 mL, is a cellulose fiber； the blood cell agglutinating agent is formed of a cationic polymer； the weight-average molecular weight of the cationic polymer is at least 10,000； and two or more kinds of the cationic polymers having different weight-average molecular weights are included.本發明之血球凝集性纖維於纖維之內部包含血球凝集劑。較佳為上述血球凝集劑對上述纖維之滲透率為2以上。上述纖維之打漿度較佳為780 mL以下，且其較佳為纖維素纖維。亦較佳為上述血球凝集劑包含陽離子性聚合物。亦較佳為上述陽離子性聚合物之重量平均分子量為1萬以上。亦較佳為包含重量平均分子量不同之2種以上之上述陽離子性聚合物。
