This report describes a method for selective removal of nucleic acids from various protein solutions, using aminated poly(γ-methyl L-glutamate) (PMLG-NH2) particles. The adsorbing activity for nucleic acids (purified DNA from salmon spermary) increased with increase in either the amino-group content or pore-size (molecular mass exclusion of polysaccharide, Mlim) of the particles. The apparent dissociation constant between the DNA and the particles (amino-group content: 3.5 meq g−1) decreased from 8.2×10−13 mol l−1 (M) to 2.0×10−13 M with increase in pore size from 2×103 to 2×105, at pH 7.0 and an ionic strength of μ=0.05. On the other hand, the adsorbing activity of bovine serum albumin increased with increasing Mlim of the particles, but decreased with increasing ionic strength of the buffer. As a result, when Mlim was 2×103 and amino-group content was 3.5 meq g−1, PMLG-NH2 particles removed DNA from various DNA-containing samples, such as protein solutions, at pH 7.0 and ionic strength (μ) of 0.2. The particles also removed DNA from crude antigen solutions originating from Bordetella bronchiseptica and Pasteurella multocida. A high recovery of protective antigen (100 %) was obtained with each sample solution after removal of the DNA, and the concentration of DNA in it decreased to below 10 ng ml−1.