Ascorbic acid is naturally occurring organic compound known to play a vital role in the human body. Since people cannot produce ascorbic acid themselves, they required it as part of their nutrition. Horticultural products are considered to be a source of the ascorbic acid in the human diet. Several analytic methods can be used for ascorbic acid determination. The use of 2,6-dichlorophenolindophenol (DPIP) as an oxidizing agent for the titration of ascorbic acid has been known as traditional technique. However, there is the possibility of error due to substance stability and the interference. So, in this paper, we optimize the spectrophotometric method for ascorbic acid quantification in Thai fruit products using DPIP. The effect of the buffering agent, the chelating agent, light exposure and the reaction time were examined. Ascorbic acid was determined in UV-Vis spectrophotometer by monitoring the pink color of indophenols dye at 518 nm which was reduced to colorless by ascorbic acid. The result showed that the metal ion interference is reduced by adding chelating agent and the stability of DPIP dye has been approved.