Astrothelium ultralucens is a species of corticolous (bark-dwelling) lichen in the family Trypetheliaceae.

The type specimen was collected by Harrie Sipman along the Carapo River (Cerro Guaiquinima [es], Bolivar) at an elevation of 800 m (2,600 ft).

The lichen has a smooth, somewhat shiny pale greenish grey thallus that covers an area of up to 7 cm (2.8 in).

Its ascospores are hyaline, spindle-shaped (fusiform) with three septa and dimensions of 105–130 by 35–42 μm.

Astrothelium ultralucens contains lichexanthone, a lichen product that causes the pseudostromata and the thallus to fluoresce yellow when lit with a long-wavelength UV light, although the thallus only weakly.