Glucagon-like peptide 1 receptor agonists (GLP-1RAs), which are currently used for the treatment of type 2 diabetes, have recently been proposed as anti-obesity drugs, due to their relevant effects on weight loss. Furthermore, dual agonists for both GLP-1R and glucagon receptor (GCGR) are under investigation for their promising action on adiposity, although underlying mechanisms still need to be clarified. We have recently demonstrated that GLP-1 and liraglutide interfere with the proliferation and differentiation of human adipose precursors, supporting the hypothesis of a peripheral action of GLP-1RA on weight. Here, we investigated glucagon activity in an in vitro model of primary human adipose-derived stem cells (ASCs). Glucagon significantly inhibited ASC proliferation in a dose- and time-dependent manner, as evaluated by cell count and thymidine incorporation. When added during in vitro-induced adipogenesis, glucagon significantly reduced adipocyte differentiation, as demonstrated by the evaluation of intracellular fat content and quantitative expression of early and mature adipocyte markers (PPARγ and FABP4, HSL). Notably, the inhibitory effect of glucagon on cell proliferation and adipogenesis was reversed by specific GLP-1R (exendin-9) and GCGR (des-His1-Glu9-glucagon(1–29)) antagonists. The presence of both receptors was demonstrated by Western blot, immunofluorescence and cytofluorimetric analysis of ASCs. In conclusion, we demonstrated a direct inhibitory action of glucagon on the proliferation and differentiation of human adipose precursors, which seems to involve both GLP-1R and GCGR. These findings suggest that the adipose stem compartment is a novel target of glucagon, possibly contributing to the weight loss obtained in vivo with dual GLP-1R/glucagon agonists.