The index closed 7.93 points lower after gaining 0.73 points on Tuesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 21.71% to VND17 trillion ($713.69 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers dropped.
GAS of state-owned Petrovietnam Gas fell 3.9%, followed by POW of electricity producer Petrovietnam Power Corporation with a 3.5% decline.
VCB of state-owned lender Vietcombank dropped 2.4% and HPG of steelmaker Hoa Phat Group closed 1.9% lower.
Seven blue chips gained, led by GAS of state-owned Petrovietnam Gas with a 1.6% increase.
Foreign investors were net sellers to the tune of VND556.35 billion, mainly selling HPG of steelmaker Hoa Phat Group and VPB of private lender VPBank.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.66% while the UPCoM-Index at the Unlisted Public Companies Market was down 0.13%.