The index closed 6.58 points lower after gaining 5.17 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange plunged by 30% to VND8.53 trillion (US$336 million), lowest since April 2023.
The VN-30 basket, comprising the 30 largest capped stocks, saw 20 tickers fell.
VRE of retail real estate arm Vincom Retail dropped 3.6%, followed by HDB of HDBank with a 2.5% decline.
CTG of state-owned lender VietinBank and MSN of conglomerate Masan Group both fell 2%.
Seven blue chips gained. BVH of insurance company Bao Viet Holdings led with a 2.6% rise, followed by PLX of fuel distributor Petrolimex, up 2.2%.
Foreign investors were net sellers to the tune of VND629 billion, mainly selling FPT of IT giant FPT Corporation and VPB of private lender VPBank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.61%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.08%.