"Inspection and quarantine units in various areas have discovered a large number of quality and safety problems with imports of US soybeans," the General Administration of Quality Supervision, Inspection and Quarantine said.
"We have reported this to the US side, demanding that it look into the causes and adopt effective measures to ensure that a situation like this does not repeat itself," it said on its website.
It detailed a series of safety problems, including the discovery of sorghum halepense and other exotic harmful weeds among the soybeans.
There was no mention in the statement of any plan to restrict or halt imports of US soybeans.
Recent global scares over the safety of China's exports -- ranging from toys to clothes to toothpaste -- have not made major headlines in the nation's state-run media.
However, frequent reports have emerged about safety problems in goods imported into China, especially from the United States.
On Monday, China said it had returned 272 heart pacemakers imported from the United States after they failed quality inspections.
The Xinhua news agency quoted the general administration as saying the pacemakers posed potential threats to patients' lives as they could cause misdiagnoses.