The index closed 6.37 points lower after gaining 11.09 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 22.82% to VND8.24 trillion ($348.30 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers dropped.
BID of state-owned lender BIDV plunged 4.5%.
SSI of leading brokerage SSI Securities Corporation fell 3% and GVR of Vietnam Rubber Group lost 2.8%.
Other decliners included STB of Ho Chi Minh City-based lender Sacombank, down 2.4%, and SAB of brewer Sabeco, down 2%.
Six blue chips gained, led by KDH of real estate firm Khang Dien House with a 3.3% rise.
It was followed by NVL of property developer Novaland Group with a 2.1% gain.
MSN of conglomerate Masan Group went up 1.1%.
Foreign investors were net buyers to the tune of VND141.64 billion, mainly buying VND of brokerage VNDirect and HPG of steelmaker Hoa Phat Group.
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 0.64%.