["Business Ethics, the Environment &Responsibility, EarlyView. ", "\nABSTRACT\nPrevious studies on the antecedents of supplier corporate social responsibility (SCSR) have mainly focused on the factors in customer‐supplier relationships, leaving the influence of suppliers' customer base underexplored. To fill the gap, this study identifies major customers' geographic dispersion (MCGD) as an important characteristic of suppliers' customer base, and explores its influence on SCSR from a combined perspective of transaction cost, social control, and signaling theories. Based on data from 1873 Chinese listed suppliers during the period from 2010 to 2021, this study finds a U‐shaped relationship between MCGD and SCSR. Moreover, the results also show that the U‐shaped relationship is further moderated by supplier size (SS) and customer concentration (CC). Overall, this study advances the understanding of SCSR and provides important implications for the participants in B2B markets and researchers alike.\n"]