Two silica gels, one modified with aminobenzenesulfonic (SABS) groups and the other with phosphate (SZP) groups, were prepared to adsorb some amino acids. Chemical analysis of the modified silica gave 0.65 mmol g(-1) aminobenzenesulfonic groups and 0.56 mmol g(-1) phosphate groups. The maximum adsorption capacities for amino acids determined by batch experiments for SABS were 1.37, 0.67, 0.76, and 0.59 mmol g(-1) for glycine, lysine, histidine, and leucine, respectively, and those for SZP were 0.75, 0.58, 0.44, and 0.75 mmol g(-1) for glycine, lysine, histidine, and leucine, respectively. The adsorption capacity of SABS was significantly affected by the solution pH, showing a higher selectivity than SZP. The materials were very stable, allowing their use several times without changes in adsorption capacity.