The index closed 9.48 points lower after gaining 2.87 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 12.73% to VND21.60 trillion ($909.12 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 22 tickers dropped.
VHM of property giant Vinhomes fell 2.9%, followed by HPG of steelmaker Hoa Phat Group and TPB of private TPBank, both with a 2.4% drop.
PLX of fuel distributor Petrolimex closed 2.1% lower.
Seven blue chips gained, led by MWG of electronics retail chain Mobile World, up 1.9%.
Foreign investors were net sellers to the tune of VND69.43 billion, mainly selling HPG and VND of brokerage VNDirect.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.64% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.15%.