The index closed 45.7 points lower after gaining 6 points on Friday. It is now hovering around the level recorded in February 2021.
Trading on the Ho Chi Minh Stock Exchange (HoSE) fell by 32.7% to VND11.53 trillion ($482.26 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 29 tickers dropped. 11 of them hit floor prices.
The biggest losers were KDH of real estate firm Khang Dien House, BID of state-owned lender BIDV, and BVH of insurance company Bao Viet Holdings, falling by around 7%.
Other declining tickers were CTG of state-owned lender VietinBank, GVR of Vietnam Rubber Group and MWG of electronics retail chain Mobile World.
VIC of biggest private conglomerate Vingroup was the only blue chip that gained 0.9%.
Foreign investors were net sellers to the tune of VND531 billion, mainly selling HPG of steelmaker Hoa Phat Group and STB of Ho Chi Minh City-based lender Sacombank.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 4.83% while the UPCoM-Index at the Unlisted Public Companies Market was down by 2.59%.