The guppy, Poecilia reticulata Peters, 1859 is an ovoviviparous freshwater fish of low waters native to the Caribbean Islands, Venezuela, Guyana, and northern Brazil. Guppies are among the most popular fishes in the aquarium trade, and they are introduced into water bodies in many parts of Brazil through the aquarium dumping. This paper reports the first record of non-native P. reticulata in water bodies at midwest Brazil. Poecilia reticulata was collected in nascent of stream Figueira located to eastern of Tangara da Serra, southwest region of Mato Grosso State. This record and the presence of juveniles suggest natural recruitment of P. reticulata in stream Figueira and the introduction this species is very worrying. Especially when we consider the studies by Krinski et al reporting that 31 species of native fish can be found in Tangara da Serra streams, and 330 species in the upper Paraguay River basin.