Megalagrion pacificum is a species of damselfly in the family Coenagrionidae. It is endemic to rivers and freshwater marshes in Hawaiʻi, especially the island of Molokaʻi. It is threatened by habitat loss. This insect was federally listed as an endangered species of the United States in 2010. Both male and female are black in color, the male with red areas on the body and the female with green. They are 34 to 37 millimeters in length.