Beijing imported almost 524,000 barrels per day, a 35% jump from the previous month.
The surge comes even as the US has asked countries to cut oil imports from Iran and threatened to impose sanctions against financial institutions doing business with Iran's energy sector.
Beijing, the biggest buyer of Iranian crude oil, defended its imports.
"China's importing of Iranian oil is based on its own economic development needs," said Hong Lei, a spokesperson for China's Foreign Ministry.
"This is fully reasonable and legitimate."
China's economic growth in recent years has seen a rise in demand for energy resources, turning it into one of the biggest consumers of crude oil in the world.
Imports from Iran are key part of Beijing's overall fuel imports.
However, it has been under pressure to cut its imports from Iran after the US threatened that firms dealing with Tehran's energy sector will be cut off from the US financial system.
China's imports from Tehran had fallen significantly in the first four months of the year, but analysts said that was mainly due to the ongoing payment dispute and low seasonal demand.
They said that with the dispute now settled, it was business as usual between the two countries.
"They are quietly carrying on as normal," Tony Regan of consultancy firm TriZen told the BBC.
Mr Regan added that Beijing was also hopeful that the US will grant it some kind of an exemption from the sanctions, not least because of the delicate nature of the US-China relations.
"The US may not want to be seen as the one challenging China on this issue," he said.

The judge in charge of the case rejected the request by prosecutors to drop the charges against the striker.
Messi and his father Jorge are accused of defrauding Spain of more than €4m (£3.1m; $5m). They deny any wrongdoing.
Lawyers acting on behalf of the tax authorities demanded 22-month jail sentences for both defendants.
Prosecutors allege that Jorge avoided paying tax on his son's earnings by using offshore companies in Belize and Uruguay in 2007-09.
Messi's lawyers had argued that the player had "never devoted a minute of his life to reading, studying or analysing" the contracts, El Pais newspaper reported earlier.
"There are rational signs that the criminality was committed by both accused parties," wrote the judge in a court filing, according to the AFP news agency.
No date has been set for the trial of the 28-year-old footballer - the four-time World Player of the Year and one of the richest athletes in the world.
In June, the high court in Barcelona ruled that Messi should not be granted immunity for not knowing what was happening with his finances, which were being managed in part by his father.
The income related to Messi's image rights, including contracts with Banco Sabadell, Danone, Adidas, Pepsi-Cola, Procter and Gamble, and the Kuwait Food Company.
Messi and his father made a voluntary €5m "corrective payment" - equal to the alleged unpaid tax plus interest - in August 2013.
China's imports of crude oil from Iran rebounded in May after the two countries resolved a payment dispute.
[NEXT_CONCEPT]
Argentina and Barcelona footballer Lionel Messi and his father should stand trial on tax fraud charges, a court in Spain has ruled.