In this paper the reaction of p-acetyl-arsenazo for determination of uran- ium ( IV) was studied. The optimum conditions were tested in the presence of Fe(ll)-CyDTA in 3 N hydrochloric acid medium. With this procedure the levels of tolerence limit of diverse ions as ZrO2+，F-，W6+，MO6+，SO42-and PO43- were higher than those with arsenazo III.