The index closed 34.23 points lower, its biggest plunge since June 20.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 39.63% percent to VND20.33 trillion ($861.79 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 29 tickers dropped.
BID of state-owned lender BIDV fell 5.6% to a five-week low.
SSI of leading brokerage SSI Securities Corporation dropped 5.1%, also to a five-week low.
VJC of budget airline Vietjet lost 4.8%, BVH of insurance company Bao Viet Holdings 4.2%, and GAS of state-owned Petrovietnam Gas 3.9%.
NVL of real estate developer Novaland Group was the only blue chip that gained with a 2.1% increase.
Foreign investors were net sellers to the tune of VND447.58 billion, mainly selling VND of brokerage VNDirect and GEE of Gelex Electric Equipment.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 3.14% while the UPCoM-Index at the Unlisted Public Companies Market was down by 1.37%.