The index closed 12.14 points lower after gaining 16.26 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 22.89% to VND21.83 trillion ($889.21 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 19 tickers dropped.
SSI of leading brokerage SSI Securities Corporation lead the decline with a 5.5% drop.
It was followed by VIC of biggest private conglomerate Vingroup, down 5.2%, and BID of state-owned lender BIDV, down 5.1%.
CTG of state-owned lender VietinBank lost 4%, and POW of electricity producer Petrovietnam Power Corporation slipped 3.9%.
Nine blue chips gained, with PDR of Phat Dat Real Estate Development surging 7% to close at ceiling price.
TCB of the largest private lender Techcombank gained 5.8%, and PLX of fuel distributor Petrolimex went up 5.1%.
Foreign investors were net buyers for the ninth straight session to the tune of VND1.02 trillion, mainly buying VHM of property giant Vinhomes and STB of Ho Chi Minh City-based lender Sacombank.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 1.06% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.76%.