Cross-linkedN,N-dimethylaminopropylacrylamide (DMP) spherical particles for the selective removal of lipopoly-saccharides (LPS) from protein solution were prepared. WhenN, N'-buthylene-bis-methacrylamide (BBMA) and divinylbenzene (DVB) were each used as a cross-linking agent and the amino-group content was adjusted to 4.0 meq g−1adsorbent or more, the DMP/BBMA and the DMP/DVB adsorbents showed good LPS adsorption at pH 7.0 and an ionic strength of μ = 0.05 to 0.2. On the other hand, the adsorption of bovine serum albumin, an acidic protein, by each adsorbent increased with the increase in the amino-group content to 4.5 mequiv. g−1adsorbent or larger, but decreased with the increase in the ionic strength (μ) of the buffer to 0.2 or stronger. Only DMP/DVB specifically adsorbed aromatic proteins such as cytochromecand myoglobin, over a wide ionic strength range of μ = 0.05 to 1.0. As a result, when the DMP/BBMA adsorbent which had an amino-group content of 4.0 meq g−1was used in conditions of pH 7.0 and μ = 0.05, LPS was selectively removed from various protein solutions, naturally contaminated with LPS.