3 percent year-on-year, while the country's trade deficit widened to 16 billion dollars, official figures showed Monday.
Inflation was 1.56 percent up from July and had reached 21.
7 percent since the start of 2008, the General Statistics Office (GSO) estimated in a preliminary report.
"The inflation figure of the first eight months of the year is still comparatively high, particularly because of the increase in the prices of oil and gas," said Ngo Tri Long, deputy director of the official Institute for Market and Prices Research.
"High inflation is now a global problem, and Vietnam is not an exception," he told AFP, adding measures to curb consumer price rises had made some progress.
Vietnam, a nation of 86 million people, had been lauded as Asia's next economic tiger.
But it has been battered in 2008 by double-digit inflation, a ballooning trade gap, tumbling share prices and worries about the banking sector and its currency, the dong.
The Vietnamese authorities have hiked interest rates and imposed stricter credit control to stem inflation, but do not expect it to fall back to single digits