Lythrum anceps (Koehne) Makino (Japanese common name: "Misohagi") is an edible plant belonging to the Lythraceae family. It is mainly distributed in Asia, Northern Africa, and Europe. Plants of the genus Lythrum exhibit a broad range of biological activities including anti-inflammatory and antimicrobial activities. Because of this, the plants are used in traditional medicine to treat hemorrhage, infected wounds, and dysentery. The activation of peroxisome proliferator-activated receptor-gamma (PPARγ) is an effective target for improving insulin resistance and anti-inflammatory activity. However, PPARγ activation by the genus Lythrum remains unclear. Aiming to evaluate PPARγ activation by L. anceps, we generated a reporter cell line using an artificial chromosome vector that stably expresses dual-color beetle luciferases. Dual-color real-time bioluminescence monitoring revealed marked PPARγ activation in L. anceps extracts. Moreover, ellagic acid was identified as a PPARγ activator present in L. anceps by a bioassay-guided fractionation approach.