The index closed 12.21 points lower after gaining 0.46 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 6% to VND20.768 trillion ($854 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 27 tickers fell.
SSB of SeABank dropped 2.9%, followed by SAB of brewer Sabeco with a 2.3% decline.
MWG of electronics retail chain Mobile World and VCB of state-owned lender Vietcombank both dropped 2.2%.
Three blue chips bucked the trend, led by POW of electricity producer Petrovietnam Power Corporation with a 1.3% rise.
Foreign investors were net seller to the tune of VND234 billion, mainly selling MBB of lender MB and VHM of property giant Vinhomes.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.69%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.22%.