The quantitative determination of the analgesic anti-inflammatory compound, 4- (anisylideneamino) antipyrine, in authentic samples, I, and capsules, II, was achieved by an accurate and reproducible analytical procedure using the PMR spectroscopy. A sensitive colorimetric method was also developed based on the azo formation using barbituric acid. The azo derivative was synthesized and identified. Experimental conditions were carefully studied. The PMR proposed method has proved to be advantageous being rapid and of a simpler manipulating technique; it helps identify the active ingredient and check its purity.