The index closed 0.6 points lower after gaining 28 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange, on which the index is based, plunged 28% to VND14 trillion ($552 million).
The VN30 basket, comprising the 30 largest capped stocks, saw 16 tickers fell.
TCB of the largest private lender Techcombank dropped 1.8% while MBB of lender MB declined by 1.3%.
VIB of Vietnam International Commercial Bank fell 1.2% and ACB of Asia Commercial Bank closed 0.9% lower.
Eleven blue chips gained. MWG of electronics retail chain Mobile World led with a 2.9% increase while FPT of IT giant FPT Corporation followed, up 2.6%.
Foreign investors were net buyers for the fourths straight session to the tune of VND466 billion, mainly selling DIG of Development Investment Construction and GAS of state-owned Petrovietnam Gas.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.13% while the UPCoM-Index for the Unlisted Public Companies Market dropped 0.04%.