Clermontia oblongifolia is a species of flowering plant in the bellflower family known by the common name Oahu clermontia. It is one of several Hawaiian lobelioids in genus Clermontia that are known as ʻoha wai. This plant is native to three of the Hawaiian Islands, where one subspecies is not uncommon but the other two are very rare and endangered. The more common subspecies, ssp. oblongifolia, is endemic to Oʻahu, where it grows in rainforests.