The index stayed in the red throughout the day and closed 2.78 points lower after gaining nearly 43 points in two recent sessions.
Trading on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, fell 8.5 percent to VND13.308 trillion ($597.85 million), lowest since last July.
The VN30 basket, comprising the 30 largest capped stocks, saw 19 tickers fell, led by TPB of TPBank with a 3.4 percent drop to a near five-month low.
It was followed by GAS of Petrovietnam Gas, down 3 percent, and SSI of leading brokerage SSI Securities, down 2.6 percent.
BVH of insurance company BaoViet and SAB of brewer Sabeco both closed 2.4 percent lower.
Seven blue chips gained, with FPT of IT giant FPT Group rising 2.4 percent and TCB of largest private lender Techcombank climbing 1.7 percent.
Other winners included VPB of VPBank, up 1.5 percent, and HPG of steel giant Hoa Phat, up 1.4 percent.
Foreign investors were net sellers to the tune of VND308.5 billion, mainly selling VHM of real estate giant Vinhomes and HQC of Hoang Quan Group.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.87 percent while the UPCoM-Index for the Unlisted Public Companies Market gained 1.3 percent.