The index closed 13.43 points lower after gaining 2.13 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 32% to VND18.45 trillion ($760 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 27 tickers fell.
VRE of retail real estate arm Vincom Retail plunged 2.7%, followed by HPG of steelmaker Hoa Phat Group and PLX of fuel distributor Petrolimex, both down 2.1%.
Three blue chips gained: BVH of insurance company Bao Viet Holdings rose 1%, while VJC of budget airline Vietjet went up 0.5% and HDB of HDBank closed 0.3% higher.
Foreign investors were net sellers to the tune of VND910 billion, mainly selling VNM of dairy giant Vinamilk and STB of Ho Chi Minh City-based lender Sacombank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 1.42%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.36%.