This study interrogates the contradiction between China’s formal diplomatic overtures in Africa and the informal, often illicit activities of its nationals engaged in illegal artisanal and small-scale mining (ASM) in Ghana and Nigeria. While China promotes a development-oriented, non-interventionist foreign policy under the rubric of South–South cooperation, recurring incidents of environmental degradation, community displacement, and regulatory violations linked to Chinese actors undermine the credibility of this narrative. Anchored in the theoretical frameworks of soft power and transnational governance, this paper employs a qualitative comparative case study methodology to analyse patterns of Chinese involvement in illegal mining across both countries. It highlights how Ghana’s relatively responsive institutional mechanisms and active civil society contrast with Nigeria’s fragmented regulatory environment and weaker enforcement. The paper argues that these discrepancies in national governance structures directly affect the diplomatic leverage and behavioural accountability of foreign actors. The findings expose the limits of China’s soft power in Africa when confronted by unregulated economic practices and state-level governance deficiencies. The paper concludes by recommending policy measures for host governments, regional institutions, and China itself to harmonise resource diplomacy with responsible conduct in the extractive sector.