The partitioning behavior of gallium ill Polyethylene glycol (PEG) (l)-ammonium sulfate (NH(4))(2)SO(4) (2) aqueous two-phase systems (ATPS) in the presence of 4-(2-pyridylazo) resorcinol (PAR) as an extractant has been investigated. The main factors, such as, pH, PEG molecular weight, PEG concentration, and temperature oil the partition coefficient (K) have been discussed. Results Show that pH has a significant effect on K. In the 20 % (mass fraction) PEG(20000)-30 % (NH4)2SO4 system, K reaches 113.43 at pH = 6.54. With the increases of PEG molecular weight and temperature, K also increases, while an increase of the PEG concentration has a negative effect oil gallium partitioning. All results were explained well according to the coordination between the -N and -O of the PAR molecule and the gallium ion and the relationship In K = A Delta w(1).