Several naturalized sheep breeds in the South American continent have little objective information available and as population size is becoming smaller the need for this information becomes more critical. The objective of this study was to differentiate between naturalized breeds in Brazil, Uruguay and Colombia using morphological descriptors and compare them with commercial breeds. The amount of 928 morphometric measurements and 2918 weights were collected. Phenotypic characterization was carried out using size, weight, colour and conformation of the animals, as well as 16 morphometric measurements of the animals. Phenotypic data were analysed using PROC GLM, CORR and PRINCOMP of Statistical Analysis System (SAS ®). The distance between breeds was carried out using morphometric and morphological data using UPGMA (Unweighted Pair Group Method Arithmetic Mean) method to create a dendrogram. Phenotypic characterization was shown to be an accessible and easy to use tool in conservation and breeding programs. The breed was the most important factor to differentiate between the animals measured, and adult weight most influenced by the environment. Commercial breeds were larger and Santa Inês animals from the Center-west and Southwest closer to Bergamasca than in other regions.