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 were 2.32, 2.50, 0.76 and 1.89 μg/mL with LOQs 7.73, 8.33, 2.55 and 6.31 μg/mL for 1st, 2nd, 3rd and 4th derivatives, respectively. LODs for SDM were 3.19, 2.59, 3.22 and 2.29 μg/mL with LOQs of 10.62, 8.63, 10.73 and 7.64 μg/mL for 1st, 2nd, 3rd and 4th derivatives, respectively. Moreover, ratio derivative method (1DD) was used for the quantification of both drugs; ranging from 10.0-25.0 μg/mL for both drugs. 1DD values were measured at 223 and 254 nm, for diaveridine and sulfadimidine, respectively. The obtained results were compared statistically by the Paired t-test and the variance ratio F-test.