Thomasomys ucucha, also known as the ucucha thomasomys, is a rodent in the genus Thomasomys of the family Cricetidae. Found only in the Cordillera Oriental of Ecuador, a mountain range, it lives in forests and grasslands at 3,380 to 3,720 m (11,090 to 12,200 ft) above sea level. It may occur with seven other species of Thomasomys. First collected in 1903, Thomasomys ucucha was formally described in 2003 and most closely resembles T. hylophilus, which occurs further to the north. Habitat destruction may threaten T. ucucha, so that it is listed as "Vulnerable" on the IUCN Red List.