<p>This study investigated effects of heat treatment on Tartary buckwheat (<i>Fagopyrum tataricum</i>) bioactivity. Ethanol extracts obtained after heat treatment were fractionated using preparative LC to obtain quercetin-derivative-rich fractions. These fractions were analyzed using LC–MS/MS and their bioactivities were evaluated. Heat treatment significantly altered the levels of quercetin and its derivatives, with the highest quercetin content observed in samples treated at 200&#xa0;°C for 40&#xa0;min, and led to significant increases in total phenolic and flavonoid contents, enhancing antioxidant activity, as measured by the DPPH assay. Furthermore, antidiabetic activity improved after heat treatment, demonstrated by increased α-glucosidase inhibitory activity and enhanced insulin sensitivity in the HepG2 cell insulin resistance model. This study highlights a simple and cost-effective approach to enhance the functional properties of Tartary buckwheat through heat treatment, supporting its potential in developing natural antidiabetic functional food materials and serving as a foundation for future research.</p>