The index closed 35.21 points lower after gaining 8.61 points on Tuesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 29.58% to VND17.62 trillion ($751.38 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 23 tickers dropped.
GVR of Vietnam Rubber Group hit the floor with a 6.9% decline.
SSI of leading brokerage SSI Securities Corporation dropped 6.7%, and VPB of private lender VPBank fell 5.9%.
MSN of conglomerate Masan Group lost 5.8%, and VHM of property giant Vinhomes closed 5.7% lower.
Seven blue chips bucked the trend, led by NVL of property developer Novaland Group with a 2.5% rise.
HDB of HDBank went up 1.9% and MWG of electronics retail chain Mobile World gained 1.3%.
Foreign investors were net buyers to the tune of VND93.35 billion, mainly selling VHM and DGC of Duc Giang Chemicals Group.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 2.89% while the UPCoM-Index at the Unlisted Public Companies Market was down by 1.20%.