Abstract: (1) According to Griess reaction, diazonium-salts formed from aromatic amines such as sulfonamides etc., react with NaNO₂ in acid medium and may be coupled with α-naphthylamine or diphenylamine to produce red colored compounds. In presence of excess NaNO₂, these red colored compounds will further Change to brownish yellow. For diazotization titration, diphenylamine is used as a good internal indicator. (2) Internal indicator may be used only in colorless solution and the end point is not sharp. (3) KBr should be added as a catalyst not only to accelerate the velocity of diazotization, but also to decrease the interaction between azo dyes and nitrous acid. (4) The indicator should be added after the addition of two-third of the amount of NaNO₂ required (the total quantities of NaNO₂ used amounted to 30ml) or before the addition of the last 5ml of NANO₂. The results thus obtained show practically no difference from these obtained by external indicator method.