Total vehicle sales, including buses and trucks, increased 5.2 percent to 1.85 million in June. That's down from 8.5 percent growth in May.
Domestic brands continued to struggle, with their share of the overall market falling 3.5 percentage points to 37.7 percent, the lowest level since 2009, according to the official Xinhua news agency.
Chinese brands are losing out as drivers increasingly favor models sold by their bigger, richer global rivals.
"China is a good market if you're just considering the sales and yield," said Zhang Xin, an analyst at Guotai Jun'an Securities in Beijing
He said the figures were better than expected given that June is traditionally a slow month for auto sales. "But the local brands don't do a good job. It's hard for them to get rid of the impression in the short term of being cheap and low quality."
Earlier, General Motors Co. said sales of GM-branded vehicles produced with its Chinese joint venture partners rose 9.2 percent to 257,798. It was the company's best ever sales performance in China for the month of June.
Nissan Motor Co., China's most popular Japanese auto brand, said sales rose 11.5 percent to 112,600 vehicles.
Ford Motor Co. said sales in the first half of the year jumped 35 percent to 407,474 as June sales rose 17 percent.