Research indicates that large auditing firms provide higher quality services to specific clients compared to smaller firms, because the economic dependence of larger firms on clients is lower. Also, in the event of auditor negligence, larger auditing firms lose more credibility than their smaller firms. The aim of this article is to investigate the factors influencing the mergers of auditing firms in Iran. In this research, a qualitative grounded theory approach has been used, and a field study was conducted using grounded theory instead of testing hypotheses, which itself contributes to understanding and constructing a theory derived from the social context and from the perspectives of the subjects. To investigate this aim, qualitative methods were used alongside 20 experts in the auditing sector with experience in the merger of audit firms, utilizing snowball sampling, and information was gathered through in-depth interviews. For analysis, the grounded theory method was utilized. In the initial stage, 123 identification codes were generated, and following revisions (removal and merging), 25 concepts were selected and results were classified into six components including organizational factors, managerial factors, extra-organizational factors, legal and regulatory factors, human resource factors, and Consequences.