Public integrity represents an increasingly visible and relevant aspect in the functioning of European Union institutions. Both the European Commission and the European Parliament have introduced measures addressing the behavioural standards of their members, often in the aftermath of damaging scandals. We analyse the ethics regulations for political actors in these two institutions (i.e., Commissioners and MEPs), focusing on the inter-related issues of conflict of interests and relations with lobbyists. We take a comparative perspective that highlights the difference in regulatory approaches between the two, which is puzzling as the ethical issues that confront Commissioners and MEPs are largely the same. Based on detailed legal analysis and expert interviews, the paper maps and explains the divergence and identifies opportunities for harmonizing rules across institutions.