The index closed 2.88 points lower after gaining 14 points in the previous two days.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 3.69% to VND15.82 trillion ($673.33 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 19 tickers fall.
VHM of property giant Vinhomes lost 2.6%, followed by VRE of retail real estate arm Vincom Retail, down 2.2%.
HDB of HDBank closed 2.1% lower and GVR of Vietnam Rubber Group lost 1.1%.
Eight blue chips gained, led by TPB of private TPBank with a 3.7% rise.
Foreign investors were net sellers to the tune of VND443.92 billion, mainly selling NVL of property developer Novaland Group and EIB of private lender Eximbank.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 0.67% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.47%.