Abstract: In the presence of reductants, the interaction between the chromophore of neocarzinostatin (NCS) and the nucleic acids yielded an adduct, In this study, we compared the effects of various reductants on the amount of adduct produced. Results supported the conclusion that in the presence of DTT, the amount of adduct produced was greatly increased, and the quality of adduct was steady. This stable adduct could be used in the investigation of its structure, thus helping to understand the mechanism of NCS to act as an anticancerous drug.