Ethical networks are an emerging form of social alliance based on collaboration between organizations that share a common ethical commitment. Grounded in a theoretical framework of virtue-based business ethics and focusing on nonprofit alliances, this study investigates the virtuousness of ethical networks; that is, how they trigger virtuous practices in their member nonprofit organizations. Adopting a qualitative grounded theory approach, the study focuses on one of the largest Italian ethical networks of nonprofit organizations operating in the social care sector. The findings show that shared ethical values and religious beliefs are positively associated with ethical network building. Based on these findings, a circular model of virtuousness is proposed in which ethical networks foster virtuous practices among their members at four levels: (1) the strategic orientation level, (2) the institutional level, (3) the organizational level, and (4) the relational level. At each of these levels, ethical networks foster a habituation to virtues and the propagation of virtuous behaviors among their members. Theoretical, practical, and social implications of the research findings are discussed.