The index closed 3.51 points lower after gaining 4.94 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 26.43% to VND22.70 trillion ($959.14 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 17 tickers dropped.
MWG of electronics retail chain Mobile World and NVL of property developer Novaland Group both gained 3.8%.
They were followed by PDR of Phat Dat Real Estate Development, up 2.1%, and SSI of leading brokerage SSI Securities Corporation, which closed 1.6% higher.
Seventeen blue chips dropped.
VHM of property giant Vinhomes fell 2.5%, and POW of electricity producer Petrovietnam Power Corporation closed 1.8% lower.
Foreign investors were net buyers to the tune of VND329.94 billion, mainly buying VNM of dairy giant Vinamilk and VHM.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.24% while the UPCoM-Index at the Unlisted Public Companies Market gained 0.05%.