The principle of impartiality, as one of the fundamental pillars of a fair trial and a guarantee of citizen rights, is considered, beyond a moral proposition, a procedural right and an institutional obligation for all actors in the trial process, including judges, bailiffs, and experts. The present study, with the aim of examining the effects of impartial trial and analyzing the challenges in ensuring it, has examined this issue with an analytical-descriptive method and relying on upstream documents and applicable laws, especially the Criminal Procedure Code and the Law on Supervision of the Conduct of Judges. The findings of the study show that observing impartiality in all stages of the trial, from obtaining evidence to issuing a verdict, plays a decisive role in strengthening the legitimacy of the judicial system, promoting public trust, and ensuring equality of arms. Also, this study, by distinguishing between independence and impartiality, argues that the lack of effective enforcement guarantees is the most important challenge to operationalizing this principle. Finally, by categorizing the enforcement guarantees of impartiality violations into three levels: criminal, disciplinary, and civil, it is explained that the full realization of impartial trial in Iran, in addition to strengthening supervisory structures, requires an analysis of the current fragmented enforcement guarantees and improving the professional culture of criminal justice agents.