The complexation of samarium(III) using 5-(20-bromophenylazo)-6-hydroxy pyrimidine-2,4-dione (Ra), 5-(40-chlorophenylazo)-6-hydroxypyrimidine-2,4-dione (Rb), and 5-(20,40-dimethylphenylazo)-6-hydroxypyrimidine-2,4-dione (Rc) was studied in the presence and absence of cetyltrimethyl ammonium bromide (CTMAB). Binary Sm-R2 and ion associate (Sm-R2)–(CTMAB) complexes were formed at pH 7.2, 7.7, and 8.2 and showed an absorption maxima at 577, 610, and 597 nm in the absence and 595, 625, and 613 nm in the presence of CTMAB, respectively. The stability constant and the stoichiometric ratio of the formed complexes were also calculated. The ion associate complex formation was completed spontaneously and the resulting complexes were stable for at least 12 h. Under the optimum experimental conditions employed, the molar absorptivity, Sandell sensitivity, optimum concentration ranges, detection, and quantitation limits were calculated. Interfering species of different anions and cations have been studied. The precision and recovery for the developed procedures are both satisfactory. The proposed procedure is successfully applied to determine samarium in standard samples of rare earth mixture, synthetic, and monazite samples.