This article has been written with the aim of seeing the impact of the chartered accountant on the sustainability of Lebanese companies. In order to respond to this problem, we have presented a general vision of chartered accountants and the importance of their intervention in a company. Then we conducted interviews with fifty chartered accountants with large experience in different regions of the Lebanese territory in order to highlight the different missions they carried out in the Lebanese companies, their role in business continuity and development, how they faced their companies' challenges, what added values they offered to them, which then led us to summarize the tasks chartered accountants saw necessary for the continuity of the companies. We also have visited twelve accounting firms and see the different stages of the accounts' auditing. A questionnaire was prepared in order to collect all needed information. We distributed it to one hundred thirty companies in different regions with the aim of seeing the role played by the chartered accountants, the missions they carried out, the essential tasks to the companies' sustainability as well as other questions enriching our study which we have presented in this article.