This paper aims at contributing to the UNESCO-IAU Astronomy and World Heritage Initiative's discussions by presenting the case study of a 20th-century observatory located in a South American country. In fact, the National Observatory of Brazil was created in the beginning of the 19th century, but its present facilities were inaugurated in 1921. Through this paper a brief description of the heritage associated with the Brazilian observatory is given, focused on its main historical instruments and the scientific and social roles it performed along its history. By way of conclusion, the paper suggests that the creation of the Museum of Astronomy and Related Sciences with its multidisciplinary team of academic specialists and technicians was decisive for the preservation of that expressive astronomical heritage.