The index closed 1.19 points lower after gaining 9.78 points on May 12.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 13.76% to VND13.62 trillion ($580.81 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 15 tickers drop.
Thirteen blue chips gained, led by VIC of Vingroup with a 5.2% rise.
Foreign investors were net sellers to the tune of VND376.52 billion, mainly selling VIC and VHM of property giant Vinhomes.
The HNX-Index at the Hanoi Stock Exchange was down 0.36% while the UPCoM-Index at the Unlisted Public Companies Market was up by 0.54%.
