Mogherini landed at Tehran’s Imam Khomeini International Airport on Friday night to join the other foreign dignitaries attending the presidential inauguration.
President Rouhani will be sworn in at the Iranian parliament on Saturday evening.
It comes after endorsement of his presidential decree by Leader of the Islamic Revolution Ayatollah Seyed Ali Khamenei on Thursday.
More than 130 ranking officials from 85 countries and international organizations will be attending the swearing-in ceremony today.
Ms. Mogherini had a major role in the nuclear talks between Iran and the Group 5+1 (Russia, China, the US, Britain, France and Germany) which resulted in the achievement of the Joint Comprehensive Plan of Action (JCPOA) in July 2015.
The parties began to implement the deal in January 2016.
The EU foreign policy chief was tasked with liaising with Iran on behalf of the Group 5+1 in the course of nuclear talks.