The decline in assets was mostly driven by markets, but funds also recorded $3.1 billion in monthly net redemptions.
Balanced funds led the way with $2.4 billion worth of redemptions, although this represented an improvement from the previous month, when funds in the balanced category had almost $3.3 billion in redemptions.
Equity fund redemptions also improved notably in August, dropping from $1.4 billion in July to $338 million.
However, the bond category saw redemptions edge higher in the month, rising from $308 million to $379 million.
Through the first eight months of the year, long-term mutual funds have now recorded $13.1 billion in redemptions, compared with $96.9 billion in net sales for the same period last year.
For ETFs, the industry trade group reported that assets declined 1.6% in August, a loss of $5.0 billion.
However, net sales were still positive for the month, at $1.5 billion, which was essentially unchanged from the previous month.
In fact, equity ETFs enjoyed a sharp turnaround in August, producing almost $1.2 billion in net sales, reversing $730 million in net redemptions the previous month.
On the other hand, bond ETF sales reversed the other way, swinging to $347 million in net redemptions, after recording $719 million in net sales in July.
The balanced and specialty categories posted modest net sales in August, with money-market ETFs adding the rest of the monthly total, $594 million worth.
Year to date, overall ETF net sales are down compared with last year, but still positive at $19.0 billion. In the same period last year, net sales totalled $40.7 billion.