Mutual funds are new financial institutions established following the enforcement of Securities Market Act and developed by the approval of The Law for Development of New Financial Instruments and Institutions. The advantages of mutual funds are clear to everyone. However, the popularity and public trust to these new financial institutions require the existence of appropriate protection mechanisms to protect the fund assets and investor’s rights. In this regard, one of the most challenging legal debates is the phenomenon of directors’ responsibilities. In Iran, there is no relevant specified statute. So in this article, I study the directors’ responsibilities in mutual funds in the United States and Britain and I will propose a legal framework for directors’ responsibilities in Iran according to the current national laws.