The index closed 9.78 points lower after gaining 9.21 points on August 16.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 22.02% to VND25.52 trillion ($1.07 billion).
Foreign investors were net buyers to the tune of VND109.89 billion, mainly buying CTG of state-owned lender VietinBank and VIC of private conglomerate Vingroup.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 1.03% while the UPCoM-Index at the Unlisted Public Companies Market was down by 1.04%.
