The index closed 10.56 points lower after gaining 5.81 points on Tuesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 6% to VND10.10 trillion ($406.29 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 22 tickers dropped.
MSN of conglomerate Masan Group plunged 6.4%, followed by MWG of electronics retail chain Mobile World with a 4.2% decline.
ACB of Asia Commercial Bank dropped 2.9%, and SSI of leading brokerage SSI Securities Corporation fell 2.7%.
Other decliners included VNM of dairy giant Vinamilk, GVR of Vietnam Rubber Group and FPT of IT giant FPT Corporation.
Five blue chips gained, including VIB of Vietnam International Commercial Bank, up 2.7%, and HPG of steelmaker Hoa Phat Group, up 2.3%.
Foreign investors were net sellers to the tune of VND251.20 billion, mainly selling HPG and KBC of industrial real estate developer Kinh Bac City.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.33% while the UPCoM-Index at the Unlisted Public Companies Market was down by 0.63%.