Peroxisome Proliferator-Activated Receptor-γ (PPARγ) is an extensively studied ligand-activated nuclear hormone receptor that functions as transcription factor and plays an important role in diverse biological processes, such as lipid metabolism and insulin sensitization. Recent studies have demonstrated that PPARγ is over-expressed in many tumor types, including breast cancer, suggesting a possible role in tumor development and/or progression and a putative prognostic value. Moreover, naturally-occurring and synthetic PPARγ agonists promote growth inhibition, apoptosis and differentiation of tumor cells. The present review summarizes the available information on PPARγ expression in breast tumors and the use of PPARγ ligands as anti-cancer agents for breast cancer treatment, both in vitro and in vivo. Considering the data so far, specific PPARγ agonists seem to exert beneficial effects against breast cancer and may therefore represent potential therapeutic agents.