Frivolous litigation is one of the fundamental challenges of civil procedure, as it not only undermines defendants’ rights but also threatens the efficiency of the judicial system through delays in proceedings and the waste of public resources. Using a descriptive, analytical, and comparative method and an institutional and functional approach, this study examines the regulatory function of the fine for frivolous litigation in the legal systems of Iran and France, with particular reference to judicial practice. The findings show that, in both systems, the fine is a regulatory measure with a punitive and deterrent function. However, in France, the fine constitutes a mature and coherent mechanism with an independent regulatory role, distinct from civil liability, extending across all stages of proceedings and supported by objective criteria for identifying abuse. By contrast, the fine in Iran serves a supplementary role in relation to compensation, its imposition depends on establishing malicious intent, and it lacks a proportionate statutory ceiling, a transparent list of evidentiary indicators, application to cassation proceedings, and effective disciplinary mechanisms. These shortcomings reduce its effectiveness and leave judicial public order vulnerable to borderline cases of abusive litigation. Accordingly, reform of Iran’s Civil Procedure Code through clarification of objective criteria, the introduction of a proportionate ceiling for the fine, and its extension to all stages of proceedings, together with the adoption of a preventive security mechanism in the French legal system, could help achieve a balance between the right of access to justice and judicial public order and improve the efficiency of the judicial systems in both countries.