Abstract: In this study, for the first time, the amount of 3-deoxy-d-erythro-hexos-2-ulose (3-DG) in fresh citrus and chestnut honeys was determined. 3-DG was measured as the corresponding quinoxalines after derivatization with orthophenylenediamine using reverse-phase high-performance liquid chromatography (RP-HPLC). Notwithstanding the freshness of the samples, high levels of 3-DG were detected in both honeys. The comparison of 3-DG and 5-hydroxymethylfurfural (HMF) concentrations, which was also quantified by RP-HPLC, showed that citrus honeys had the lowest amount of 3-DG (107 mg/kg) and the highest of HMF (16.7 mg/kg), while chestnut honeys had the opposite (398 and 1.2 mg/kg, respectively). During thermal treatment, different 3-DG and HMF trends were highlighted between the citrus and chestnut honeys; at the end, 3-DG formation was more favored with respect to HMF formation. Moreover, in citrus honeys, a good correlation between 3-DG and HMF levels was observed, which was not found in chestnut honeys, suggesting a role of the high pH values of these honeys on the degradation routes. The kinetic analysis showed the highest k value for 3-DG and HMF formation in chestnut and citrus honeys, respectively. The lowest Ea values related to 3-DG formation and the highest to HMF formation, indicating that the key intermediate 3-DG is easily formed at low temperatures, whilst the formation of HMF requires higher temperatures. For this reason, 3-DG seems to be an aging index rather than a thermal index and its use, at least for honeys at high pH values, together with HMF, could improve their quality assessment.