Cyclic voltammetry has been applied for studying the cathodic reduction behaviour of 3-azo-[4-(diazin-2-yl)-benzene- sulphonamido-] -1-oxa-4-thia-spiro (4,5) decan-2-one sodium salt, as azo dye sulpha drug at the hanging mercury electrode in different supporting electrolytes, i.e. perchlorate, acetic acid-acetate buffer, nitrate and phosphate, at different pH values ranged from (1–11) and different ionic strengths (0.01–0.15). The two related compounds for the sodium salt of azo dye sulpha drug have been also studied at 0.1 M acetic acid- sodium acetate buffer (pH ∼ 3.45). Direct current stripping voltammetry (DCSV) has been used for the determination of the drug under investigation. The effect of the different parameters e.g. initial potential, scan rate, …etc. has been tested. The detection limit has been determined for azo dye salpha drug and its related compounds. Relative standard deviation at the 1 × 10−5M level was 2.9%. The method was applied to the determination of the compounds in urine sample.