Dugesia japonica, belonging to Platyhelminthes, plays an important role in the animal evolution and is well known for its extraordinary regenerative ability. Mitogen activated protein kinase (MAPK) pathway is an important cell signaling pathway that converts extracellular stimuli into a wide range of cellular responses. The MAP-extracellular signal-regulated kinase (MEK) is a main component of MAPK/ERK signaling, but there are few studies on mek gene in planarians. In this study, we observe the expression patterns of Djmek1 and Djmek2 in planarians, and find that both of the two genes are required for the planarian regeneration. At the same time, we also find that both Djmek1 and Djmek2 are involved in the planarian regeneration by regulation of cell proliferation and apoptosis. Together, our findings show that the functions of the two genes are similar and complementary, and they play an important role in the regeneration of planarians. (C) 2020 Elsevier Inc. All rights reserved.