New contracts fell 0.6 percent compared with July, federal statistics authority Destatis said, disappointing analysts' predictions of a 0.6-percent increase.
In a year-on-year comparison, orders were down 6.7 percent on August 2018's level.
"The weakness in demand continues in industry. Activity will remain muted for now," the economy ministry said in a statement.
Looking in more detail at the data, orders fell only 0.3 percent month-on-month when counting out large contracts for items like aircraft - a volatile element that can distort the overall figure.