The index closed 1.27 points lower after gaining 11.50 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 24% to VND15.61 trillion (US$626 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 14 tickers fell.
HPG of steelmaker Hoa Phat Group and VNM of dairy giant Vinamilk were the top losers, both went down 1.5%.
MBB of lender MB fell 1.4% and GVR of Vietnam Rubber Group closed 1.3% lower.
Twelve blue chips gained.
SSB of SeABank led with a 4.8% rise, followed by VRE of retail real estate arm Vincom Retail, up 4.2%.
TCB of the largest private lender Techcombank increased by 1.6% and CTG of state-owned lender VietinBank closed 1.2% higher.
Foreign investors were net sellers to the tune of VND472 billion. They mainly net sold CTG and HPG.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 0.02%, while the UPCoM-Index for the Unlisted Public Companies Market went up 0.01%.
MSCI's broadest index of Asia-Pacific shares outside Japan was mostly flat.
European shares opened slightly higher, with the STOXX 600 index gaining 0.3%, helped by retail after a subdued session for Asian indexes.