Abstract: The distribution of rhenium ion the binary aqueous phase extraction system of polyethylene glycol 2000 (PEG) and ammonium sulfate was studied photometrically by the color reaction of Re(Ⅶ) with 4-(2-pyridylazo)-resorcinol (PAR). A definite amount of standard Re(Ⅶ) solution was added to the binary aqueous phase extraction medium containing 3 mL of 300 g·L-1 PEG solution, 3 mL of 300 g·L-1 (NH4)2SO4 solution and 1 mL of 1 g·L-1 PAR solution, and buffered to pH 6.5 with PBS. The solution was made up to 10 mL, shaked for 5 min and equilibrated in a water bath at 30 ℃ for 20 h. After cooling to room temperature and phase separation, the absorbance of the lower phase was measured at 540 nm. Its Re content was found from the standard curve and the rate of extraction (E%) was calculated. It was found that acidity of the extraction medium was the most influential factor to the extraction efficiency as compared with other factors.