Ilex mesilauensis is a tree in the family Aquifoliaceae, native to Borneo. It is named for the Mesilau area of Sabah.
Ilex mesilauensis grows up to 15m (49feet) tall. The bark is fissured, with big lenticels. The leathery leaves are obovate or spatulate and measure up to long. The inflorescences are in spikes.
Ilex mesilauensis is endemic to Borneo, where it is known only from a single location on the Mesilau River near Mount Kinabalu in Sabah. Its known habitat is in lower montane forests, at elevations of around .