The index closed 12.52 points lower after gaining 1.36 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 79% to VND29.327 trillion (US$1.16 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 17 tickers fell.
GVR of Vietnam Rubber Group saw the biggest decline of 6.9%, followed by POW of electricity producer Petrovietnam Power Corporation with 6.7% drop, and PLX of fuel distributor Petrolimex, down 4.5%.
Nine blue chips gained. TCB of private lender Techcombank went up 4.4%, MBB of lender MB Bank increased by 4.0%, and HDB of HDBank closed 1.8% higher.
Foreign investors were net buyers to the tune of VND549 billion, mainly buying FPT of IT giant FPT Corporation and MWG of electronics retail chain Mobile World.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 1.64%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.98%.