Customers are increasingly talking positively about brands that are socially responsible and authentic. However, little empirical research has related corporate social responsibility (CSR) to brand authenticity and brand authenticity to customers’ positive word-of-mouth. Moreover, although highly attractive alternative brands are increasingly appearing in the marketplace, there is a lack of research examining the role of alternative attractiveness in the relationship between CSR and brand authenticity. We address these shortcomings in the literature drawing on data from 1,101 customers of insurance services brands and analyze them using structural equation modeling. The findings show that CSR is positively related to customers’ positive word-of-mouth, both directly and indirectly, through brand authenticity. Moreover, alternative attractiveness positively moderates the effect of CSR on brand authenticity. This implies that CSR can act as a differentiation mechanism to further enhance the focal brand’s authenticity, when an alternative brand is perceived as highly attractive.