The index closed 9.78 points lower after gaining 9.21 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 22.02% to VND25.52 trillion ($1.07 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 19 tickers fell.
VIC of private conglomerate Vingroup dropped 4.9%, followed by VHM of property giant Vinhomes with a 3% decline.
VRE of retail real estate arm Vincom Retail fell 2.9% and STB of Ho Chi Minh City-based lender Sacombank closed 1.7% lower.
Ten blue chips were in the green.
SSI of leading brokerage SSI Securities Corporation gained 3.8% while FPT of IT giant FPT Corporation rose 1.1%.
Foreign investors were net buyers to the tune of VND109.89 billion, mainly buying CTG of state-owned lender VietinBank and VIC of private conglomerate Vingroup.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 1.03% while the UPCoM-Index at the Unlisted Public Companies Market was down by 1.04%.