The index closed 59.99 points lower after gaining 18.4 points last Friday.
Trading on the Ho Chi Minh Stock Exchange increased by 39% to VND33.567 trillion (US$1.33 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 29 fall.
MSN of conglomerate Masan Group saw the steepest drop, down 7.0%, while BID of state-owned lender BIDV slid 6.93% and SSI of brokerage SSI Securities Corporation closed 6.92% lower.
BCM of Becamex Investment and Industrial Development fell 6.89%, followed by GVR of Vietnam Rubber Group with a 6.87% decline and VRE of retail real estate arm Vincom Retail with a 6.83% decrease.
Only one blue chip gained, which was SHB of the Saigon - Hanoi Commercial Joint Stock Bank, up 0.4%.
Foreign investors were net seller to the tune of VND1.24 trillion, mainly selling CTG of state-owned lender VietinBank and MBB of state-owned MB Bank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 4.82%, while the UPCoM-Index for the Unlisted Public Companies Market went down 2.44%.