The color-substance, C9H9O5N2K, (III) was successfully isolated from the Janovsky reaction-mixture of acetone, m-dinitrobenzene (I), and potassium hydroxide. The spectral and chemical properties were studied in comparison with the potassium salt of 2, 4-dinitrobenzyl methyl ketone (V), the Meisenheimer-like complex structure of III being thus confirmed : Absorption spectra of III and V in acetone were quite identical with those of the Janovsky and the Zimmermann reaction-mixture, respectively (Fig. 1) ; λmax of III varied highly in different solvents, in contrast to that of V (Table I). NMR spectrum gave the sextet structure of the proton (Hδ) attached to the ring sp3 hybridized carbon atom (Table II). When the solution of III was kept at pH 1, diacetonyl-dinitroazoxybenzene, V, and I were isolated. Strong alkali decomposed III to 2, 4-dinitrophenol and unknown substances ; a remarkable difference from V was shown as for the elimination of nitrite ion. Ultra-violet irradiation on III gave the unknown substance, free of carbonyl absorption in IR spectrum.