To investigate rutin hydrolysis in dough made with ‘Manten-Kirari’, a new Tartary buckwheat variety with trace rutinosidase activity that lacks bitterness, we performed a time course study of the residual rutin ratio in dough at different water contents and blending ratios of Tartary buckwheat flour. In the common rutinosidase variety, ‘Hokkai T8’, a large portion of the rutin was hydrolyzed within 30 min after the addition of water, whereas about 80–90% remained in the dough made with ‘Manten-Kirari’. We also investigated the residual rutin ratio in noodles such as soba-noodle and pasta containing Tartary buckwheat flour. With ‘Hokkai T8’, rutin was hydrolyzed almost completely in all noodles tested. In contrast, about 90% of rutin remained in ‘Manten-Kirari’-containing noodles. In addition, while ‘Hokkai T8’ noodles exhibited strong bitterness, ‘Manten-Kirari’ noodles lacked or had only slight bitterness. These results indicate that ‘Manten- Kirari’ holds promise as a material for rutin-rich noodles with minimal bitterness.