Eucommia constans is an extinct species of flowering plant in the family Eucommiaceae. Eucommia is a genus of small trees now native to China, with a fossil record that shows a much wider distribution. E. constans is known from fossil fruits found in Miocene to Pleistocene deposits of east-central Mexico. E. constans is one of five described fossil species from North America assigned to the modern genus Eucommia. The other species are E. eocenica, E. jeffersonensis, E. montana, and E. rowlandii.