Abstract: A new colour reaction of the molybdenum with salicylfluorone and cetyl trimethyl ammonium bromide has been studied. In a dilute hydrochlpride acid medium (0.2-0.8N) molybdenum can form a red-colour tenary complex with the above-mentioned reagents. The complex exhibits maximum absorption at 530nm, and the value of apparent molar absorption coefficient is found to be 1.40×10⁵. The constituent of the complex is also established as Mo:SAF:CTMAB = 1:2:2 by the methods of isomolar continuous variation and slop ratio, as well as triple diagram.Ahigh sensitive and selective spectrophotometric method is developed for the determination of molybdenum. The Beer's law is obeyed in the range of 0-8μg Mo/25ml. Most metal ions do not interfere with the determination of molybdenum. Oxidized metal ions, such as Fe(III), Cr(VI), V(Y) and Mn(VII), must be reduced with ascorbic acid. The ions of tin (IV) were reduced by sodium hypophosphite in the presence of mercuric ions as catalyst. The ions of zirconium were masked by EDTA. Only the ions of tungsten and titanium interfere seriously. The method is used in the determination of molybdenum in some high alloy steel with satisfactory results.