The index closed 6.25 points lower after gaining 25.51 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 6% to VND27.96 trillion ($1.13 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 26 tickers fell.
MWG of electronics retail chain Mobile World dropped 2.7%, followed by MSN of conglomerate Masan Group with a 2.5% decline.
CTG of state-owned lender VietinBank fell 2% and BCM of Becamex Investment and Industrial Development declined by 1.9%.
Four blue chips gained. GAS of state-owned Petrovietnam Gas rose 2.5% and VIC of private conglomerate Vingroup increased by 2.1%.
Foreign investors were net sellers to the tune of VND912 billion, mainly selling VHM of property giant Vinhomes and VNM of dairy giant Vinamilk.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.62%, while the UPCoM-Index for the Unlisted Public Companies Market went up 0.10%.