The basic extraction study on the separation of fission product molybdenum-99 and uranium in sulfuric acid solution by tri-n-octylamine in kerosene has been investigated. The equilibration time and the effect of temperature, concentration of extractant, uranium and sulfuric acid concentration on this extraction system were examined. The optimum conditions for the coextraction of molybedum-99 and uranium have been obtained with the overall recovery of 90% for99Mo and greater than 99% for uranium. Based on the complex stability difference between UO2(VI) and MoO2(VI) with TOA, uranium in the organic phase can be back-extracted by proper chloride concentration. On the other hand, molybedum-99 can be stripped from the organic phase by sodium carbonate or ammonium hydroxide solution.