The option clause is not defined in the law, but it can be stated that when the subject of a transaction is more than one thing and the buyer has the right to choose one of the objects, this discretion is known as the option clause. The duration of the option clause is three days, and the holder of the option must choose one of the objects, which is a maximum of three, as the subject of the transaction. The main question is whether the option clause is among the cases that grant the right to terminate the contract to the other party, and what is the position of this clause in the legal systems of Iran and Afghanistan? Understanding the position, source, and method of incorporating this clause into contracts in the legal system of Afghanistan and explaining its position in the legal system of Iran, considering that this institution is not explicitly accepted in the Iranian legal system, are the main objectives of this research. The findings of this study show that there is no explicit textual evidence for the option clause in the Quran and Sunnah, and it is merely based on the ijtihad (independent reasoning) of the Hanafi and Maliki jurists. This institution has many similarities with suspensive conditions, which are recognized in foreign law. Although the option clause is not explicitly provided for in the Iranian legal system, it can be inferred from certain provisions of Iranian civil law that the option clause can be implied in contracts under certain conditions. It seems that the option clause can be accepted based on the provision of Article 216 of the Civil Code, which recognizes the principle of the autonomy of the will. This research is analytical and descriptive in nature and relies on library research and documentary sources.