Buckwheat sprouts are a popular food item in many countries. The effects of light-emitting diodes (LEDs) on sprout growth and development, changes in mRNA transcription, and accumulation of phenylpropanoid compounds were studied in tartary buckwheat 'Hokkai T8' sprouts. The highest transcript levels were observed after 2 days of LED exposure for all genes, especially FtPAL and FtF3'H, which showed higher expression in sprouts grown under blue and white light than in those grown under red light. Catechin content in sprouts grown under red light increased dramatically throughout the 10 day time course. Maximum rutin content (43.37 mg/g dry weight (DW)) was observed in sprouts at 4 days after exposure (DAE) to blue light. Similarly, the highest cyanidin 3-O-rutinoside content (0.85 mg/g DW) was detected at 10 DAE to blue light. On the basis of these results, blue LED light is recommended as a light source for enhancing the content of phenolic compounds in tartary buckwheat sprouts.