The purpose of the present invention is to provide: a porous fiber that exhibits both improved adsorption capacity, and suppressed exposure and detachment of particulates； an adsorption column filled with said porous fiber； and a blood purification system in which an adsorption column is connected to a water removal column. In order to achieve this purpose, the porous fiber according to the present invention has the following constitution. Specifically, the porous fiber according to the present invention has a three-dimensional pore structure formed by a solid fiber, and satisfies all of the following conditions. (1) The porous fiber has particulates having a diameter of not more than 200 [mu]m, and the percentage of area occupied by said particulates having a diameter of not more than 200 [mu]m in a horizontal cross section of the three-dimensional pore structure is at least 3.0%. (2) The porous fiber does not contain said particulates having a diameter of not more than 200 [mu]m in the region within 1.0 [mu]m in the depth direction from the outermost surface.本發明之目的在於提供一種兼顧粉粒體之露出或剝離之抑制與吸附性能之提昇的多孔質纖維、填充有該多孔質纖維之吸附管柱、及將吸附管柱與除水管柱連結而成之血液淨化系統。為了達成上述目的，本發明之多孔質纖維具有以下之構成。即，其係具有由實心形狀之纖維所形成之三維細孔構造，且滿足以下所有必要條件之多孔質纖維：(1)含有直徑200μm以下之粉粒體，且上述直徑200μm以下之粉粒體於上述三維細孔構造之橫截面中之面積佔有率為3.0%以上；(2)於自最表面於深度方向1.0μm以內之區域中不含上述直徑200μm以下之粉粒體。
