Abstract: The mechamisms of oxidation of p-nitrotoluene to p-nitrobenzoic acid with dioxygen in NaOH-CH₃OH solution were proposed and investigated. It was hypothesized that reaction mechamsms were that p-nitrotoluene firstly formed p-nitrobenzyl anions as a result of the action of strong alkali NaOH and anions formed were oxidized by dioxygen activated by metal phthalocyanine catalysts to form p-nitrobenzyl acid through a series of free radical reactions. By studying the catalytic action of metal phthalocyanine catalysts and the cocatalytic action of NaOH and combining them with other experimental results, the impontant intermediates such as p-nitrobenzyl anions et al. were indirectly proved, and the mechanisms hypothesized were also indirectly confirmed.