To provide a method for efficiently oxidizing an organic substrate with oxygen under such a condition that the decomposition of the imide compound is inhibited.

This method for oxidizing an organic substrate comprises contacting the organic substrate with oxygen in ht presence of an N-hydroxy cyclic imide and ≤0.1 mol%, based on the organic substrate, of transition metal compounds consisting of at least two compounds selected from cobalt compounds, cerium compounds, titanium compounds, iron compounds and copper compounds.