The index closed 1.11 points lower after gaining 0.96 points on July 18.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 5.52% to VND17.69 trillion ($748.29 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 19 tickers dropped.
Eight blue chips gained, led by HDB of HDBank with a 2.4% rise.
Foreign investors were net buyers to the tune of VND226.98 billion, mainly buying VNM of dairy giant Vinamilk and VHM of property giant Vinhomes.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 0.22% while the UPCoM-Index at the Unlisted Public Companies Market was down by 0.06%.
