The subject of this article is to analyze the rights of the complainant in competition investigations. The question whether complainant is a party to investigation is not the subject of the article. The study is composed of three chapters including the Conclusion. The first part of the study analyzes the EC practice. The analysis indicates the general direction of both the Commission's practice as well as the legal doctrine. The second part of the study questions the position of the complainant in Turkish Competition Law. This section presents the role of the complainant under four sub-titles. The first sub-title is the role of the complainant in the pre-investigation phase. The second is the role of complainant within the investigation. The third is role of complainant in the decision phase. And the last sub-title is the role of the complainant following the decision.