This work describes the modification of silica gel with dimethylglyoxime, in order to prepare an effective sorbent for the preconcentration and determination of copper. The sorption capacity of dimethylglyoxime-modified silica-gel (DMGMS) was 71.37 mg g(-1) and the optimum for the quantitative recovery of copper was found to be 5.0. The optimum flow rate, sorbent amount, and sample volume were 1 mL min(-1), 300 mg, and 50 mL, respectively. 10 mL of 0.1 mol L-1 HCl was the most suitable eluent. The detection limit of copper was 6.0 ng mL(-1). The recommended method, for the determination of copper, is simple and reliable, without any notable matrix effect and can be successfully applied to environmental water samples. Copper recovery in the range from 99-100% was obtained from seawater and thermal spring water using this method. The method was applied to standard reference materials, NIST-1515 (apple leaves) and NIST-1643e (simulated fresh water), for the determination of copper and the results were in good agreement with certified values.