New spectrophotometric method was proposed for the rapid and accurate determination of Ce(III) using a new synthesized sulfacetamide azo-dye reagent [N-(4-((2,3-dihydroy-5-(3,5,7-trihydroxy-4-oxo-4H-chromen-2-yl)phenyl)diazenyl) phenylsulfonyl)acetamide] [DTPPA]. The reagent was characterized by IR, 1HNMR and mass spectra. The developed method was based on the reaction of Ce(III) with DTPPA reagent to form brown colored complex in an alkaline medium using borate buffer at pH = 9 with absorption maximum at 560 nm. The method was enhanced by the use of cationic surfactant of cetylpyridinium bromide (CPB). Different factors affecting the formation and stability of the complex such as reagent concentration, time, temperature, solvents and order of addition were also studied. The composition of the complex was found 1:2 (metal: ligand) by both Job's and molar ratio methods. The stability constant of the complex was calculated to be 3.387×106. Beer's law was obeyed in the concentration range of 5.0-100 µg mL-1 of Ce(III) with molar absorpitivity and Sandell's sensitivity 1.020×104 L mol-1 cm-1 and 0.01373 µg cm-2, respectively. The proposed method was applied for the determination of micro-amounts of Ce(III) in some industrial and plant samples. The Ce(III) complex was also prepared in the solid state.