The study investigated the impact of cross-border arms smuggling and its threat to regional cooperation and peacebuilding in Katsina State, Nigeria. The aim of the study was to assess how illegal arms trafficking across Nigeria's northern borders influences security dynamics and undermines peace initiatives in the region. The scope of the study covered cross-border areas of Katsina, focusing on the role of arms smuggling in exacerbating conflicts, violence, and insecurity. The study adopted a qualitative methodology, utilizing interviews with security officials, local community leaders, and border control personnel, along with analysis of secondary data from government reports and security assessments. The theoretical framework of the study was based on the Security and Development Framework, which explores the relationship between illicit arms trade, regional security, and sustainable peace. The findings of the study revealed that cross-border arms smuggling significantly contributes to the proliferation of violence, particularly in conflict-prone areas, and poses a severe threat to peace-building efforts in Katsina and the wider northern region. The study concluded that the illegal arms trade undermines security, fosters instability, and complicates regional cooperation aimed at resolving conflicts. Therefore, the study recommended enhanced border security, regional cooperation in intelligence sharing, and a robust legal framework to combat arms trafficking and promote sustainable peace.