The index closed 8.51 points lower after gaining 9.49 points on Friday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 2.07% to VND10.50 trillion ($447.81 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 21 tickers fall.
NVL of property developer Novaland Group plunged 5.2%, followed by MSN of conglomerate Masan Group with a 3.4% decline.
MWG of electronics retail chain Mobile World lost 3.3% and PDR of Phat Dat Real Estate Development fell 3.2%.
Six blue chips rose, led by ACB of Asia Commercial Bank with a 2.1% gain.
Foreign investors were net sellers to the tune of VND326 billion, mainly selling VNM of dairy giant Vinamilk and CTG of state-owned lender VietinBank.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was up 0.32% while the UPCoM-Index at the Unlisted Public Companies Market was down by 0.64%.