Alkaline oxidative cracking with molecular oxygen was demonstrated as an effective method to depolymerize lignin under moderate conditions. Ammonia-extracted lignin from corn stover was depolymerized to aromatics and organic acids by the alkaline oxidation. The identified products by GC-MS, NMR, and HPLC included monoaromatic compounds (such as vanillin, p-coumaric acid, vanillic acid, acetovanillone etc.) and organic acids (such as oxalic, acetic, formic acids, etc.). The overall mass yield of quantified aromatics and organic acids varied from 24% to 58% under the investigated conditions. It was found that the yields and compositions of the products were determined by the reaction conditions (temperature, reaction time, and oxygen pressure). More vanillin and organic acids were produced with oxygen under high temperature and long time, while p-coumaric acid was the primary product under oxygen deficient condition.