The liquid-liquid extraction behavior of 2-ethylhexyltolylsulfoxide (EHTSO) towards uranium(VI) contained in nitric acid aqueous solution has been investigated. It was found that the extraction increases with increasing nitric acid concentration up to 5.0 mol/l and then decreases. Extraction also increases with increasing extractant concentration. The extracted species appears to be UO2(NO3)2.2EHTSO. The influences of temperature, NH4NO3 and Na2C2O4 concentrations on the extraction equilibrium were also investigated and the thermodynamic functions of the extraction reaction were obtained.