The index closed 8.24 points lower after gaining 0.81 points on Tuesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 6.45% to VND21.71 trillion ($914.16 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 27 tickers dropped.
VHM of property giant Vinhomes dropped 3.5% and GVR of Vietnam Rubber Group lost 2%.
MWG of electronics retail chain Mobile World and VNM of dairy giant Vinamilk both fell 1.9%.
Only two blue chips gained. STB of Ho Chi Minh City-based lender Sacombank went up 4.7% and HPG of steelmaker Hoa Phat Group closed 2.2% higher.
Foreign investors were net buyers to the tune of VND339.76 billion, mainly buying HPG of steelmaker Hoa Phat Group and MSN of conglomerate Masan Group.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.08% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.17%.