Abstract: (±)-2-(6-Methoxyl-2-naphthyl)-propionic aldehyde has been oxidized to the corre-sponding acid with hydrogen peroxide by use of selenium dioxide as catalyst instead of Tollen's reagent. The optimum conditions obtained are reported in this paper:catalyst/aldehyde=0.01(wt), aldehyde/absolute ethyl alcohol=0.20(wt/vol), water content in the reaction medium <3%, H₂O₂/aldehyde=1-1.2(mol), reaction tempera-ture and time:10-15℃ for 5 days. The yield of acid was 73.13%. less than that by silver nitrate method. Content of Se in the product ≤ 3ppm.