The index closed 1.14 points lower after gaining 4.49 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 3.34% to VND11.53 trillion ($491.29 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 16 tickers gain.
GAS of state-owned Petrovietnam Gas and VCB of state-owned lender Vietcombank both lost 1.1%.
GVR of Vietnam Rubber Group fell 0.9%, followed by MWG of electronics retail chain Mobile World with a 0.8% decline.
Ten blue chips gained, led by NVL of property developer Novaland Group with a 3.8% rise.
PDR of Phat Dat Real Estate Development closed 1.5% higher and VPB of private lender VPBank went up 1.3%.
Foreign investors were net buyers to the tune of VND122.67 billion, mainly buying VND of brokerage VNDirect and SSI of leading brokerage SSI Securities Corporation.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 0.24% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.37%.