The Program of Agro-pastoral Development and Promotion of Local Initiatives in South-eastern Tunisia (French acronym PRODESUD) is an agro- pastoral development project implemented since 2003 in southern Tunisia by Tunisian government and the International Fund for Agriculture Development (IFAD). The principal mission assigned to PRODESUD was to promote participatory and sustainable management of rangelands and water resources and ensure better integration of livestock and agriculture (IFAD, 2002). Thus, PRODESUD has encouraged tribal communities of southern Tunisia to join new community-based organizations (GDAs) built up on socio-territorial units that correspond to the traditional tribe boundaries. The principal hypothesis that emerges is the next: to what extent the changes made by PRODESUD throughout the period 2003-2020 have contributed to improving or degrading the governance of tribal rangelands in southern Tunisia. This paper aims mainly to explore the governance system of those rangelands using Ostrom’s Design Principles (DP) for sustainable governance of common-pool resources (Ostrom, 1990, 2000, 2009). We start by analyzing institutional change induced by PRODESUD. Such analysis refers to the Institutional Grammar Tool (IGT) developed by Crawford and Ostrom, (1995, 2005). In our case, IGT enables to identify rules codified in contracts signed between PRODESUD with community-based organizations, which includes the new ones (GDAs) and the Land Management Councils of the tribes, mainly about promoting the rest technique locally called “Gdel”. In addition, IGT allows classifying those new rules with the consistent classification of Institutional Analysis and Development (IAD) Framework’s rules typology, which enables a better understanding of the institutional change enhanced by PRODESUD. We move next to discuss conformity of new management rules supported by PRODESUD with Ostrom’s Design Principles. The conducted investigation shows an interesting fit ensured by PRODESUD’s institutional prescriptions between the requirements of good governance identified by Ostrom (1990, 2000, 2009) and the harsh setting of southern arid rangelands in Tunisia.