"The two sides decided to increase by three times the current trade volume of around $6 billion (5.2 billion euros) to $18 billion," Rouhani said in a joint televised press conference.
"We also spoke about tourism, direct flights between Seoul and Tehran, and Korean investment in Iranian tourism infrastructure, including building hotels," he added.
Park is the first South Korean president to visit Iran since the two countries established diplomatic relations in 1962, and as Seoul seeks new markets to turn around a lengthy decline in export revenues.
Her three-day visit comes just months after a historic nuclear deal with world powers lifted sanctions crippling Iran's economy in exchange for limits on its nuclear programme.
Park, who is accompanied by several ministers and a 230-strong business delegation, will also be received by Iran's supreme leader Ayatollah Ali Khamenei.
The two countries have pledged to develop their relations in the energy sector.
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"We will expand relations in energy projects and infrastructure... and in oil, gas, railways and ports," Park said.
Tehran hopes this month to increase its oil exports to Seoul to 400,000 barrels per day from a current 100,000 bpd, according to Oil Minister Bijan Zanganeh.
The two governments signed 19 cooperation documents in the presence of the presidents, and further memorandums of understanding were due to be signed by the private sector, Rouhani said.
Talks also included discussions about the situation on the divided Korean peninsula amid fears that Pyongyang is preparing to conduct a fifth nuclear test.
"The security of the Korean peninsula and security of the Middle East are very important to us," Rouhani said.
"We seek peace and stability in the Korean peninsula and categorically oppose building any weapons of mass destruction."
Park said she "explained South Korea's opinion on... nuclear disarmament of North Korea... and requested Iranian cooperation".