The index closed 1.82 points lower after gaining 17.09 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 15% to VND26.14 trillion ($1.06 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 18 tickers fell.
VRE of retail real estate arm Vincom Retail dropped 4.7% while VHM of property giant Vinhomes closed 2.3% lower.
BID of state-owned lender BIDV declined by 1.7% and POW of electricity producer Petrovietnam Power Corporation fell 1.3%.
Nine blue chips gained, led by MSN of conglomerate Masan Group with a 3.1% rise, followed by SSI of leading brokerage SSI Securities Corporation, up 2.5%.
Foreign investors were net sellers to the tune of VND389 billion, mainly selling VHM and MSB of Vietnam Maritime Commercial Bank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.12%, while the UPCoM-Index for the Unlisted Public Companies Market went up 0.09%.