With the increasing demands from society towards sustainable and social responsible business practices, management for sustainable development has become a cornerstone to understand the success of many firms in the current competitive context. This article investigates corporate social responsibility (CSR) and examines the links between CSR practices and business outcomes – both financial and non‐financial (i.e. image and corporate reputation) – for small‐to‐medium sized enterprises (SMEs). In addition, we also attempt to determine whether the impact of such relationships is moderated by firm size. To this end, we carry out a quantitative study using PLS techniques to analyze a sample of SME owners and managers, with a view to test the proposed model in the light of social capital theory. In this sense, our study is pioneering in that it aims to determine – from a quantitative viewpoint – the degree to which firm size has a moderating impact on a series of relevant CSR‐driven outcomes. The data suggest that, in SME contexts, CSR impacts corporate reputation, brand image and financial value of the company. Importantly, we find that the larger the firm, the greater the intensity of the relationships linking CSR and business outcomes. Hence, our findings have important implications for CSR implementation in SME contexts. Finally, we provide a series of guidelines aimed at maximizing the effectiveness of CSR‐based business practices. Copyright © 2017 John Wiley & Sons, Ltd and ERP Environment