The index closed 2.15 points lower after gaining 4.68 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 27% to VND15.17 trillion ($596 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 15 tickers fell.
POW of electricity producer Petrovietnam Power Corporation led the decline with a 3.6% loss.
It was followed by PLX of fuel distributor Petrolimex, down 2.6%, and TCB of the largest private lender Techcombank, down 2.3%.
Ten blue chips gained, with BVH of insurance company Bao Viet Holdings posting the biggest increase of 2.8%.
Foreign investors were net sellers to the tune of VND1.14 trillion, mainly selling FPT of IT giant FPT Corporation and TCB of the largest private lender Techcombank.
They have been net selling for 16 consecutive sessions.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.16%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.38%.