Carbohydrates and ginsenosides in ginseng are biologically interrelated. Their synchronous analysis is therefore essential in chemical research on ginseng to characterize its “holistic” quality. Here we investigated the processing chemistry of red ginseng (RG), a ginseng product processed by water-steaming, for which both carbohydrates and ginsenosides were qualitatively and quantitatively determined through multiple analytical techniques. Results revealed that the steam-processing not only qualitatively and quantitatively altered the ginsenosides but also affected the polymeric carbohydrates via changing their physiochemical parameters, i.e. water-solubility, molecular size, types and ratios of constituent monosaccharides. Potential mechanisms involved in the transformation of ginseng chemicals are proposed and discussed, including hydrolysis (deglycosylation, demalonylation, deacetylation), dehydration, polymerization, volatilization, reduction and the Maillard reaction. The study strengthens the research on the processing chemistry of RG, and therefore should be helpful for elucidating the scientific basis of RG preparation and application.