By the spectrophotometric method the complex formation of bismuth(III) with 2,3,4-try­hydroxy­phenilazo-5'-sulphonaphtalin in the presence and the absence  of cationic surface-active substance – cetylpyridinium bromide has been investigated. It was defenied that in the presence of cetylpyridinium bromide the mixed ligand complex Bi(III)–R–CPBr forms. With this, it was observed batochrom shift in absorb spectrums and its maximum yield shifts to more acidic medium comparatively with the same complex of Bi(III)–R. There  was determined the influence of the reacting components, time and temperature on complex formation of binary and mixed ligands complexes. It is shown that determination of Bi(III) with 2,3,4-tryhydroxyphenilazo-5'-sulphonaphtalin in the presence of cetylpyridinium bromide highly selectivity. Elaborated methods were applied for the determination of microquantities of bismuth(III) on the lead base alloy of A 263-3-mark