The index closed 3.6 points lower after gaining 12.1 points on Tuesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 18.6% to VND8.27 trillion ($337.62 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 17 tickers dropped.
HPG of steelmaker Hoa Phat Group and MSN of conglomerate Masan Group both dropped 2.4%.
STB of Ho Chi Minh City-based lender Sacombank and VRE of retail real estate arm Vincom Retail both fell 2.3%.
Other losers included GAS of state-owned Petrovietnam Gas, KDH of real estate firm Khang Dien House and GVR of Vietnam Rubber Group.
Nine blue chip gaines, with VIB of Vietnam International Commercial Bank rising 2.3%.
CTG of state-owned lender VietinBank rose 0.9%, and FPT of IT giant FPT Corporation went up 0.8%.
Foreign investors were net sellers to the tune of VND82.22 billion, mainly selling HPG and SSI of leading brokerage SSI Securities Corporation.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.53% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.44%.