The index closed 2.07 points lower after gaining 1.22 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 6% to VND12.09 trillion (US$475 million).
Foreign investors net sold VND669 billion, mainly withdrawing from FPT of IT giant FPT Corporation and MWG of electronics retail chain Mobile World.
The VN-30 basket, comprising the 30 largest capped stocks, saw 25 tickers fell.
FPT of IT giant FPT Corporation fell the steepest with a 1.3% drop.
MWG of electronics retail chain Mobile World declined by 1.1% and VRE of retail real estate arm Vincom Retail closed 0.9% lower.
Five blue chips gained, including VHM of property giant Vinhomes with a 0.9% rise.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.07%, while the UPCoM-Index for the Unlisted Public Companies Market went up 0.14%.