Hyloxalus mystax is a species of frog in the family Dendrobatidae. It is endemic to Ecuador where it is only known from its type locality on the Cordillera del Cóndor at 1,830 m (6,000 ft) asl. It is a little known species not observed since 1972.
Males measure 19.5–21.5 mm (0.77–0.85 in) and females 19.2–22.8 mm (0.76–0.90 in) in snout–vent length. They have scattered darkspots on the abdomen. Males have pronounced black stippling on the throat. The male call is a rapid series of chirps.
