The index closed 29.7 points lower after gaining 26.1 points on Wednesday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 18% to VND11.12 trillion ($465.77 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 28 tickers dropped.
GVR of Vietnam Rubber Group and MWG of electronics retail chain Mobile World both plunged 6.8%.
SSI of leading brokerage SSI Securities Corporation dropped 6.7%, and STB of Ho Chi Minh City-based lender Sacombank fell 6.5%.
Other declining tickers include HPG of steelmaker Hoa Phat Group, down 6.2%, and POW of electricity producer Petrovietnam Power Corporation, down 5.8%.
VIC of biggest private conglomerate Vingroup was the only winner with a 0.2% rise.
Foreign investors were net sellers to the tune of VND131.66 billion, mainly selling HPG and PHS of Phu Hung Securities.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 2.89% while the UPCoM-Index at the Unlisted Public Companies Market was down by 1.65%.