The index closed 1.17 points lower after gaining 5.95 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 23.99% to VND8.69 trillion ($370.20 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 15 tickers fall.
VIC of private conglomerate Vingroup dropped 2.7%, followed by BVH of insurance company Bao Viet Holdings with a 2.2% decline.
VNM of dairy giant Vinamilk lost 2.1% and VRE of retail real estate arm Vincom Retail closed 1.8% lower.
Thirteen blue chips ended in the green.
PDR of Phat Dat Real Estate Development gained 5%, followed by SAB of brewer Sabeco with a 1.8% rise.
PLX of fuel distributor Petrolimex went up 1.5% and MSN of conglomerate Masan Group closed 1.3% higher.
Foreign investors were net sellers to the tune of VND298.83 billion, mainly selling VIC of private conglomerate Vingroup and VHM of property giant Vinhomes.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 0.01% while the UPCoM-Index at the Unlisted Public Companies Market was down by 0.76%.