The index closed 6.26 points lower after gaining 3.09 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 18% to VND25.42 trillion ($999 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers fell.
VJC of budget airline Vietjet fell 2.9% and VHM of property giant Vinhomes closed 1.9% lower.
VRE of retail real estate arm Vincom Retail lost 1.8% and GVR of Vietnam Rubber Group declined by 1.7%.
Eight blue chips gained, led by POW of electricity producer Petrovietnam Power Corporation with a 3.7%, and PLX of fuel distributor Petrolimex, up 3%.
Foreign investors were net sellers to the tune of VND1.8 trillion, mainly selling FPT of IT giant FPT Corporation and VHM of property giant Vinhomes.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.34%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.61%.