To simplify the spectrophotometric determinationof micro amount of vanadium in sea water, the use of N-benzoyl-N-phenylhydroxylamine (BPA) has been studied. As the effect of large amount of iron(III) was examined, it was found that the absorbance of BPA-vanadium (V) complex decreased slightly with increasing amount of iron(III) until the amount of iron 1000 times as much as that of vanadium was reached. The effects of the concentration of various acids, potassium permanganate and BPA in the presence of large amount of iron(III) were also examined. On the basis of the results of experiments, water samples were analyzed as follows; 50mg of iron(III) was added to 2(-5) 1 of filtered sea water. Vanadium was coprecipitated with iron (III) hydroxide at pH 6 to 7. The precipitates were dissolved in a small amount of 2N H2SO4. Vanadium was oxidized to quinquevalent state with 0.2 ml of 3% KMnO4 solution. After the reduction of excess permanganate with ethanol, the solution was diluted to 25 ml with 3N HCl. Vanadium was extracted with 10 ml of 0.1% BPA-CHCl3 solution. The absorbance of CHCl3 solution was measured at 530nm against water. The recovery of vanadium from sea water was determined radiochemically, and found to be(93.6±2.1)%. The content of vanadium in sea water collected from the seas near the Bonin Islands and Yoron Island were found to be 1.3 and 0.8μg/l, respectively.