To remove endotoxin (lipopolysaccharide; LPS) from a protein solution used as drugs, various aminated cellulose beads were prepared by immobilization of diaminoalkanes, polyethyleneimime or poly(ε-lysine) onto cellulose beads (Cellufine). The LPS adsorption capacity of the aminated Cellufine depended strongly on the bead pore size (molecular mass exclusion; Mlim) but not necessarily on their amino-group content. The larger the Mlim of the beads, the larger was the LPS adsorption capacity. As a result, when the adsorption of LPS was measured by a column method at pH 7.0, μ=0.17, only poly(ε-lysine)-immobilized Cellufine (pore sizes Mlim 5×104) selectively removed LPS from a bovine serum albumin (BSA) solution contaminated with LPS: the residual concentration of LPS in the BSA solotion was <0.1 EU/mL (<10 pg/mL), and the recovery of the BSA was 98%.