Sustainability is more and more becoming a critical success factor for firms; the shared value and business case for sustainability conceptions can support business model change or innovation towards sustainable business models (SBM). Small firms are the most spread organizational model worldwide and can play a relevant role in terms of economic and social development. The corporate social responsibility literature have often depicted small business as less engaged and more constrained with respect to environmental and social practices. This paper aims to translate the organizational size debate in the field of SBM, by analyzing small and large firms’ perceptions about their drivers to business case and their implementation constraints towards a more sustainable business model.