A greening phenomenon has been observed in some plant foods such as chestnut, sweet potato,burdock, and others during processing. The formation of the pigments was postulated as reactions of primary amino compounds with chlorogenic acid or caffeic acid ester, yielding acridine derivatives. Acridine derivatives have been regarded as mutagenetic agents. For the reason, the bacterial reverse mutation test was carried out to evaluate the genotoxicity of green pigment using Salmonella typhimurium TA98 and TA100. Alanine, arginine, aspartic acid, glycine,lysine, and phenylalanine were reacted repectively with chlorogenic acid to synthesize model compound. Green pigment was extracted from sweet potato. Maximum concentration of 2 and 50 mg/plate was tested for the synthetic green pigments and extracted green pigment respectively, taking bacterial survival, solubility, and color intensity into consideration. There was no signigicant increase in the reverse mutation either with or without S9 activation system by any test material. Though further studies with other genotoxicity test system are necessary, both synthetic and sweet potato green pigments seemed not to cause mutation despite the acridine moiety in their structures.