Leucostethus fugax, also known as Pastaza rocket frog, is a species of frog in the family Dendrobatidae. It is endemic to the eastern slopes of the Cordillera Oriental, southern Ecuador. Although originally only known from the valley of Pastaza River, it is now known to be more widespread. Its known range extends close to the Peruvian border and its true range may include Peru.
Adult males measure NaN1NaN1 and adult females NaN1NaN1 in snout–vent length. Toes have basal webbing. An oblique lateral stripe is present and reaches the eye. The venter is immaculate cream. Adult males have a conspicuously swollen third or fourth finger.
Leucostethus fugax inhabits moist forests in a transition zone between humid tropical forest and very humid premontane forest at elevations of 210m–700mm (690feet–2,300feetm) above sea level. It can occur in both secondary and primary forest. It is threatened by habitat loss caused by agriculture and logging. It is present in the Podocarpus National Park. Its range overlaps with, although it has not been recorded there.