This paper presents a succinct reconstruction of the segmental phonology of Proto-Maweti-Guarani, the hypothetical protolanguage from which modern Mawe, Aweti and the Tupi-Guarani branches of the Tupi linguistic family have evolved. Based on about 300 cognate sets from the authors' field data (for Mawe and Aweti) and from Mello's reconstruction (2000) for Proto-Tupi-Guarani (with additional information from other works; and with a few changes concerning certain doubtful features, such as the status of stem-final lenis consonants *r and *ß, and the distinction of *c and *č ), the consonants and vowels of Proto-Maweti-Guarani were reconstructed with the help of the traditional historical-comparative method. The development of the reconstructed segments is then traced from the protolanguage to each of the modern branches. A comparison with other claims made about Proto-Maweti-Guarani is given in the conclusion.