The index closed 4.24 points lower after gaining 12.37 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 5% to VND11.011 trillion ($448.12 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 22 tickers fell.
VNM of dairy giant Vinamilk dropped 1.8%, followed by CTG of state-owned lender VietinBank, down 1.7%.
STB of Ho Chi Minh City-based lender Sacombank lost 1.5% and BCM of Becamex Investment and Industrial Development closed 1.3% lower.
Eight blue chips gained, led by VIC of private conglomerate Vingroup with a 2.9% rise.
Foreign investors were net seller to the tune of VND558 billion, mainly selling VIC and DCM of Petro Vietnam Ca Mau Fertilizer.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.82% while the UPCoM-Index for the Unlisted Public Companies Market gained 0.04%.