Social networks have become an inevitable and integrated part of daily routine for many people. People can freely express their opinions and feelings on almost everything in a large crowd. In this research, we investigate the opinions of the public in relation to one of the most challenging topics in the current international affair: The Iran deal. The deal was reached between Iran and the world powers (China, Russia, United Kingdom, United States, and the European Union in July 2015. As a result of the agreement, Iran agreed to restrict its conflicting program in exchange for lifting some of the restrictions. The viability of the agreement, however, is highly at risk. To analyze the public opinion about the deal, we extracted relevant tweets and performed sentiment analysis by two different approaches (lexicon-based and machine-learning). The results show that the largest number of tweets contained positive sentiments followed by negative and neutral.