Abstract: The effect of alkali concertrations on the preparation of p-nitrobenzoic acid by oxidation of p-nitrotoluene with dioxygen in liquid phase was ivestigated. As it turned out, the yields of p-nitrobenzoic acid increased with the alkali concentrations increased. p-nitrobenzoic acid in 8.1% yield with a purity more than 98.0% was obtained by using alkali concentration of 4.8 mol/L and methanol as a solvent at 50℃. 2.0Mpa O₂ pressure for 12 hrs.