The index closed 5.25 points lower after gaining 4.07 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 26% to VND7.51 trillion (US$296 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers fell.
HDB of HDBank was the biggest losing ticker with a 4.1% decline, followed by BCM of Becamex Investment and Industrial Development, down 1.5%.
SSI of brokerage SSI Securities Corporation lost 1.2% while CTG of state-owned lender VietinBank fell 1.1%.
Seven blue chips gained, led by PLX of fuel distributor Petrolimex with a 1.8% increase.
VHM of property giant Vinhomes went up 1% while VIC of private conglomerate Vingroup gained 0.6%.
Foreign investors were net sellers to the tune of VND439 billion, mainly selling STB of Ho Chi Minh City-based lender Sacombank and VNM of dairy giant Vinamilk.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.03%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.48%.