Invasive plant species (IPS) management in national parks is a complex problem often characterized by the involvement of various organizations with different responsibilities, legal mandates, and jurisdictions. These institutional arrangements shape the structure, function, and decision-making behaviors of organizations and influence management effectiveness. Drawing on institutional theory, this study analyzed institutional arrangements and how these influenced IPS management in Vietnam’s national parks. Data were collected between May and July 2017 using in-depth interviews with 39 key informants with responsibility for IPS management at different institutional levels (national, provincial, and local national parks). Results demonstrated that IPS management in Vietnam’s national parks was characterized by centralized management with overlaps and gaps in vertical institutional relationships that limited the effectiveness of horizontal relationships. These characteristics resulted in a lack of clear guiding regulations and limited resources that restricted decision making and hindered implementation at the local national park level. The study highlights the need for a common set of principles across agencies, governed by an overarching body to promote constructive relationships across the vertical and horizontal institutional dimensions of IPS management.