The agreement covers the construction of the second phase of the Kangan Petro Refining Company.
"The financing of this project will be finalized within nine months at the rate of 95 percent ... by South Korean banks," said Asghar Arefi, the Iranian official who signed the accord, according to Shana news agency.
Arefi said the first phase of the Kangan project was 30 percent completed with an investment of nearly 120 million euros.
Back in May, Tehran and Seoul signed 19 memorandums of understanding at a high-profile ceremony in Tehran, attended by the two countries’ presidents.
Cabinet ministers and senior officials from the two countries signed the documents as part of efforts to boost the relations between Tehran and Seoul.
The deals are meant to boost bilateral collaborations in a range of fields, from maritime transportation to cultural and academic issues.