AbstractResearch SummaryWe examine whether acquisitions affect the divestment of firms' alliance‐based relational assets. Using data from the biopharmaceutical industry and a matched case–control research design, we find that alliances are more likely to be terminated following acquisitions compared to alliances not subject to acquisitions. This higher termination likelihood is driven by acquisitions where the acquirer's alliance management capacity is stressed, and by alliances inherited from targets. The inherited alliance effect is attenuated by the target's partner's common connections with the acquirer but amplified by the target's partner's unique connections outside the merging firms' alliance portfolios. These findings are consistent with our relational view‐based theorizing on the post‐acquisition challenges of retaining alliance‐based assets, contributing to corporate strategy scholarship on alliances and acquisitions.Managerial SummaryIn many industries, firms' portfolios of interorganizational alliances enable them to realize novel complementarities and, thereby, enhance their performance. In such sectors, managers also frequently acquire other organizations to obtain access to critical resources. However, what managers may overlook is that acquisitions can destabilize existing alliance relationships. In this study, we show that the acquiring firm's capacity to effectively manage alliance‐based assets is stressed once it inherits the target firm's alliances. In general, target firm alliances become more challenging to sustain, and, in particular, those that hold a higher potential for novelty become more unstable. Consequently, when evaluating acquisitions, managers should look beyond obvious measures of a target alliance's value and assess the post‐acquisition integration challenges that may threaten its stability.