As a concept challenging the growth paradigm, degrowth is put into practice in different ways. Ones of which are degrowth-oriented cooperatives: organisations composed of producers and consumers that intend to keep a locally oriented focus and embrace more responsible economic practices to promote socio-ecological sustainability. Despite their flourishing relevance, a robust understanding of their functioning is still missing. This becomes essential to comprehend how they differ from normal cooperatives and support their diffusion. Therefore, this work investigates the internal organisational dynamics in a degrowth cooperative through a case study. We used a participatory system dynamics modelling approach involving the cooperative’s members to develop a causal-loop model describing the cooperative’s main functioning. Several dynamics appeared to take place within the cooperative, reinforcing ones favouring cooperative growth and balancing ones limiting its expansion. While growth dynamics and conflict emergence resemble normal cooperatives’ behaviour, limiting mechanisms, depending on the local focus and the potential setting of income sufficiency thresholds, are expected to prevent the cooperative from excessive expansion and lose its degrowth ethos. Moreover, the participatory modelling method used appeared to contribute to improving the members’ understanding of the problems, identifying shared solutions, and enhancing communication. This study's contribution is two-fold: first, it reports the organisational dynamics of a cooperative practising degrowth and, second, highlights how participatory modelling can be a powerful tool in those contexts to increase members’ engagement and enhance communication.