The statistics released Friday could have an effect on the presidential election, observers say.
Before August, an average of more than 150,000 jobs were added each month.
Economists had been expecting at least 125,000 new jobs in August.
In his speech accepting the Democratic Party's nomination to seek re-election, President Barack Obama said he had "a real, achievable plan that will lead to new jobs, more opportunity and rebuild this economy on a stronger foundation."
The Mitt Romney campaign released a reaction to Obama's speech before it was even delivered, assailing Obama as having failed to create enough jobs, cut the deficit in half or increase incomes.
Economist and columnist Peter Morici said the unemployment rate fell to 8.1 percent only because large numbers of potential workers quit looking for work "and are no longer counted in the official jobless tally."
"The most effective jobs program appears to be to convince working-aged adults they don't need a job," he said.
The jobs report said 2.6 million persons were "marginally attached to the labor force." The category includes people who "wanted and were available for work," but had not looked for a job in the past four weeks and were, therefore, cut out of the data that applies to the unemployment rate.
The job figures were more eagerly anticipated in economic and political circles than most because they arrived six days before the Fed meets to decide if it will take new measures to stimulate the economy and two months ahead of the Nov. 6 presidential election.
Many labor economists surveyed said they expected the economy would add 125,000 to 127,000 jobs in August, a smaller gain than the 163,000 jobs added in July, which was the largest gain since February.
They also predicted no change in the 8.3 percent U.S. unemployment rate.
Automatic Data Processing Inc. said Thursday the U.S. economy added 201,000 non-farm private sector jobs July to August. The payroll firm also revised its June-to-July report upward from 163,000 jobs to 173,000.
The U.S. unemployment rate has been above 8 percent for 42 months. The average length of joblessness for those who remain in the labor force was 39 weeks in July, a 15-month low, Labor Department statistics indicated.
The Labor Department has two more jobs reports before the presidential election, including one Nov. 2, four days before Election Day.