The aim of the study was to select the variety most suitable for producing buckwheat juice from buckwheat leaves. We harvested six common buckwheat varieties (USA, Japan HS4251, Daegwan, Daewon, Daesan, and Yangjul buckwheat) before they entered the reproductive growth period. The leaves were freeze-dried and used for extraction. We determined the phenylpropanoid content using high performance liquid chromatography (HPLC). The Daegwan variety has the highest phenylpropanoid content such as chlorogenic acid, caffeic acid, epicatechin, ferulic acid, rutin, quercetin, and kaempferol. The phenylpropanoid content in the Daegwan variety is 1,542.9 μg/g which is 1.5 times higher than other varieties. So, it was selected as a suitable variety for producing buckwheat juice using buckwheat leaves. Thus, buckwheat leaves of Daegwan variety were used for extraction with hot water at 60, 70, 80, 90 and 100°C for 3 h determine the optimal extraction temperature. As a result, we found out that the amount of rutin and total phenylpropanoids was the highest when buckwheat leaves were extracted with hot water at 60°C. Therefore, Daegwan variety is suitable for the development of functional extracts using the buckwheat leaves with the highest phenylpropanoid content.