Novel silica gel-immobilized rhodamine (SGR) anchored by hydrazinium hydrate was synthesized. The selectivity and adsorption ability of the SGR for metal cations were investigated with fluorophotometry and atomic absorption spectrophotometery, respectively. The SGR exhibits high selectivity and adsorption capacity for Hg2+. The maximum static adsorption capacity of the SGR for Hg2+ was 25.8 mu mol g(-1). The linear response range covers a concentration range of Hg2+ from 20 ppb to 2000 ppb and the detection limit is 10 ppb. The determination of Hg2+ in real water samples displays satisfactory results, and the SGR can be used repeatedly by treating with a solution of tetrabutylammonium hydroxide.