Using plate screening method, a moderately halophilic strain LYG1-1 was isolated from seawater sample offshore of Sanya. According to physiological and biochemical characterizations, 16S rRNA sequences and phylogenetic analysis, cells were Gram-negative. It grew best at 30℃, pH 7.5 and with the presence of 10% NaCl. Phylogenetic analysis based on 16S rRNA gene sequence showed that it belonged to the genus Halomonas, having the highest similarity (99.72%) with Halomonas salina. The maximum esterase activity was observed at 45℃, pH 8.0. The effects of various divalent cations were studied based on the activity of esterase from Halomonas sp. The concentrations of 5 mmol·L^-1 Mg²⁺ and Ca²⁺ enhanced the esterase activity of LYG1-1, while the presence of Hg²⁺ strongly inhibited its activity.