The Iraqi Oil Ministry said 2.48 million barrels of oil were exported in May, compared to 2.62 million bpd in April.
Ministry spokesman Asim Jihad said last weekend in a statement emailed to China's official Xinhua news agency bad weather near the southern port city of Basra and attacks on a pipeline to Turkey were to blame for lower exports.
The Chinese National Petroleum Co. has stakes in three Iraqi oil projects, which have a combined output of about 1.6 million barrels of oil per day. Chinese officials in January said the political situation in Iraq handicapped the country's full energy potential.
Iraq depends on oil revenue for 95 percent of its federal budget. China, meanwhile, is eager to secure more energy supplies as its economy expands.
Iraqi violence has increased steadily since U.S. combat forces left the country in 2011. Disputes over oil laws between the semi-autonomous Kurdish government in the north and the central government in Baghdad have clouded further oil export potential.