This paper presents a comparative analysis of the verb system of the three known Zamucoan languages, namely Old Zamuco, described by the Jesuit father Ignace Chomé in the first half of the eighteenth century, plus Ayoreo and Chamacoco, still actively spoken in the Chaco area between Bolivia and Paraguay. The analysis has confirmed the internal consistency of this language family, allowing us to build a plausible reconstruction of the Proto-Zamucoan verb system. The analysis has unsurprisingly pointed out Old Zamuco as the most conservative language among the three; Chamacoco, by contrast, appears to be the most innovative. This notwithstanding, Chamacoco also has conservative features that turn out to be particularly relevant for the purpose of linguistic reconstruction.