The aim was to determine conditions under which rutin can be retained during production of Tartary buckwheat (Fagopyrum tataricum) dough. Tartary buckwheat flour was hydrothermally treated by mixing with water at 25, 40, 60, 80 and 95 °C, with unprocessed Tartary buckwheat flour as control. With hydrothermal treatments at 25, 40 and 60 °C, most of the rutin was transformed to quercetin. However, for hydrothermal treatments at 80 and 95 °C, rutin was retained due to denaturation of the rutin-degrading enzymes during hydrothermal treatment. This is the first report to describe a temperature threshold for denaturation of rutin-degrading enzymes in any buckwheat material. Tartary buckwheat dough produced at 95 °C contained 12 mg rutin/g dry matter. Based on these characteristics, dough from hydrothermally treated Tartary buckwheat is a promising, rutin-rich functional food material.