A spectrophotometric method for the assay of dapsone based on the chromophore formation after reaction with 1,2-naphthoquinone-4sulphonic acid sodium salt was developed. The reaction proceeded quantitatively at pH 2 and 60oC within 30 minutes when the molar ratio of reagent to dapsone was 10. After completion of the reaction, formed derivative (dapsone- NQ) was extracted from the aqueous solution with chloroform/ n-butanol (3:1). Dapsone- NQ shows maximum absorbance at 440 nm. The absorbance is linear (r=0.9999) over 2-30 µg.ml-1 concentration range. The proposed method has been successfully applied to the determination of dapsone in tablets and the results were compared with those obtained by the USP XX method using t- and F- tests. Keywords :