A highly sensitive luminescent reaction is proposed for the determination of submicrotraces of boric acid by complexation with dibenzoylmethane in ether‐concentrated sulfuric acid. The optimal conditions of complex formation between boric acid and dibenzoylmethane are investigated, luminescence spectral caracteristics of the solutions of the complex are described, and the phosphorescence mean lifetime of the dibenzoylmethane‐boric acid system is evaluated. Analytical curves, established by fluorimetry and phosphorimetry, are satisfactory. 0.0005 μg B/ml is the minimum detectable concentration.