Seoul brought 1,032,938 tons of Iranian crude oil last month, or 244,240 barrels per day (bpd), compared with 570,338 tons imported a year ago, the data showed, reported Reuters.
In the first three months of the year, the world's fifth-largest crude importer brought 2,956,497 tons, or 699,068 bpd, of crude from the Middle Eastern country against 1,401,138 tons in the same period in 2015, according to the data.
Iran, which seeks to regain its market share after the lifting of sanctions in January, told OPEC it raised output last month by a minor 15,000 bpd to 3.40 million bpd.
The world's biggest oil producers will meet in Doha on Sunday to discuss a proposed output freeze at January's levels.
Iranian Oil Minister Bijan Namdar Zanganeh will not attend the meeting, but will send a representative.
In total, South Korean imported 11.52 million tons of crude last month, or 2.72 million bpd. The total was four percent higher than the 11.12 million tons imported in March of 2015, customs data showed.
Final data for last month's crude oil imports will be released by state-run Korea National Oil Corp later this month.