Derivative spectrophotometry for two sulfa drugs (Diaveridine and sulfadimidine) was carried out for their simultaneous quantification in their binary mixtures. The optimum conditions were studied. The zero crossing wavelengths for Diaveridine (DV) in presence of sulfadimidine (SDM) were 235, 273, 242, 258, 244 nm, 238 and 289, 224 nm for 1st, 2nd, 3rd and 4th derivatives, respectively. The linear range for DV was 2.5-35.0 μg/mL and that for SDM was 1.0-25.0 μg/mL. LODs for DV