The index closed 10.3 points lower after gaining 10.9 points on Friday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 34% to VND9.55 trillion ($392.8 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 18 tickers falling.
VIC of biggest private conglomerate Vingroup plunged by 6.2%, followed by VHM of property giant Vinhomes with a 4.6% drop.
Other declining tickers included KDH of real estate firm Khang Dien House, HDB of HDBank and VCB of state-owned lender Vietcombank.
Eight blue chips gained, led by POW of electricity producer Petrovietnam Power Corporation with a 3.2% rise.
STB of Ho Chi Minh City-based lender Sacombank rose 2.8%, and GAS of state-owned Petrovietnam Gas went up 1.5%.
Foreign investors were net buyers for the seventh session in a row to the tune of VND235.75 billion, mainly buying VNM of dairy giant Vinamilk and DGC of Duc Giang Chemicals Group.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 0.63% while the UPCoM-Index at the Unlisted Public Companies Market was down by 0.19%.