Abstract: In this study,the effects of monosaccharide types on the formation of advanced glycation endproducts (AGEs) in the monosaccharide-lysine model systems were investigated. The pH,reaction color,substrate consumption,AGEs intermediates (glyoxal,GO;methylglyoxal,MGO;3-deoxyglucosone,3-DG;fructoselysine,FL),and AGEs (Nε-(Carboxymethyl) lysine,CML;Nε-(Carboxyethyl) lysine,CEL;pyrraline,Pyr) in glucose-,galactose-,fructose-and sorbose-lysine heated at 120℃ for 0~120 min were discussed. The results showed that the pH decrease and the color increase degree in aldose systems were higher than that in ketose systems as the reaction progressed. At the end of reaction,the loss of lysine in the glucose-lysine (Glu-Lys),galactose-lysine (Gla-Lys),fructose-lysine (Fru-Lys) and sorbose-lysine (Glu-Lys) systems were 26.65%,28.95%,11.47% and 14.90%,respectively;The loss of monosaccharides in all model systems was more than 75.00%,which was much higher than that of lysine. In the simulated system,aldehyde-ketone conversion occured in monosaccharides,but the ratio was less than 10%. The contents of GO and 3-DG in all model systems were decreased with the increase of heating time,which indicated that GO and 3-DG were abundantly formed within 20 min.The formation of α-dicarbonyl compounds was much higher than that of FL. When the reaction was end,the content of CML and CEL in ketose systems was higher than that in ketose systems. The AGEs level was in the order of CEL > CML > Pyr. This paper indicates that it is necessary to focus on the intermediate pathways,especially α-dicarbonyl compounds,for study the formation and inhibition of AGEs in the future research.