A bacterial strain A1 was isolated from activated sludge that treat with hapersaline waste water and identified as Arthr obacter sp. this strain was capable of growing on MM with the NaCl contents 0.1 mol L^-1~2.0 mol L^-1 and phenyl acetic acid as the sole source of carbon and energy. The osmoregulation mechanism of this strain was studied, it was found that the intracellular accumulation of K⁺;free amino acid;QAC increased with the increasing of salinity. The intracellular amino acid and QAC contents increased immediately when salt was added suddenly to culture to a final content of 1.0 mol L^-1. The contents of amino acid and QAC increased by 2.1 times and 4.9 times respectively in 40 minutes.