One of the important issues in Iranian judicial practice is the filing of a “concurrent” complaint during the course of a previously filed complaint under investigation, which results in the realization of parallel proceedings. This issue is important in terms of hearing or not hearing a “concurrent” criminal lawsuit. The basic question of the present research is as follows: in the case where a complaint bearing the aforementioned characteristics is discovered by a judicial authority either when an objection is raised by the accused, what judicial decision should be rendered by the court to which the case has been subsequently referred, or by the branch where the later-filed claim is being adjudicated? The legislator has raised and determined the issue of objection of antecedent in legal matters in the “second paragraph” of Article 84 and Articles 89 and 103 of the Civil Procedure Code approved in 1379, but such clarity is not observed in the Criminal Procedure Code. Therefore, there is a divergence of opinion in judicial practice regarding matters previously subject to criminal proceedings. It appears that, in order to uphold justice, and to prevent parallel proceedings and issuance of conflicting judgments, concurrent criminal actions are absolutely inadmissible and shall not be heard or prosecuted, and The most appropriate decision is for the competent judicial authority to issue an order to discontinue or prosecution. "The authors examine the subject through a descriptive-analytical approach.