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 µm, and the percentage of area occupied by said particulates having a diameter of not more than 200 µm 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 µm in the region within 1.0 µm in the depth direction from the outermost surface.
