The index closed 19.10 points lower after gaining 14.12 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 52% to VND35.53 trillion ($1.39 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 26 tickers fell.
BCM of Becamex Investment and Industrial Development fell 4.2%, followed by FPT of IT giant FPT Corporation with a 4.1% decrease.
SSI of leading brokerage SSI Securities Corporation dropped 4% and VJC of budget airline Vietjet closed 3.1% lower.
Four blue chips gained, including ACB of Asia Commercial Bank with a 2.8% rise and GVR of Vietnam Rubber Group, up 1.7%.
Foreign investors were net sellers to the tune of VND1.5 trillion, mainly selling PVS of PetroVietnam Technical Services Corporation and MCH of Masan Consumer Corporation.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 2.10%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.81%.