The index closed 9.66 points lower after gaining 5.78 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 3% to VND18.54 trillion ($732 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers fell.
POW of electricity producer Petrovietnam Power Corporation dropped 6.3%, followed by GVR of Vietnam Rubber Group, down 4.3%.
BVH of insurance company Bao Viet Holdings fell 2.7% and BID of state-owned lender BIDV closed 1.6% lower.
Nine blue chips gained. TPB of private TPBank increased by 2.2% and MBB of lender MB rose 2%.
Foreign investors were net sellers to the tune of VND347 billion, mainly selling FPT of IT giant FPT Corporation and VHM of property giant Vinhomes.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.81%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.86%.