The index closed 7.77 points lower after gaining 10.15 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange rose 0.03% to VND21.826 trillion (US$858.8 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 23 tickers fell.
GVR of Vietnam Rubber Group saw the biggest drop of 2.63%, followed by FPT of IT giant FPT Corporation with a 2.55% decline and MWG of electronics retail chain Mobile World, down 2.4%.
Only six blue chips gained. PLX of fuel distributor Petrolimex grew 1.2%, MBB of lender MB Bank went up 0.7%, and VCB of state-owned lender Vietcombank closed 0.6% higher.
Foreign investors were net seller to the tune of VND1.042 trillion, mainly selling VCB of Vietcombank and FPT of FPT Corporation.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.37%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.35%.