It closed the morning session 23.4 points lower in its fourth losing session in a row, having fallen 38.6 points Friday.
The VN30 basket, comprising the 30 largest capped stocks, saw 28 tickers in the red.
VRE of retail real estate arm Vincom Retail plunged the deepest with a 6.5% decline, followed by STB of Ho Chi Minh City-based lender Sacombank, down 6.3%.
GVR of Vietnam Rubber Group dipped 6% while MWG of electronics retail chain Mobile World lost 5.9%.
Other losers included TCB of the largest private lender Techcombank, TPB of private TPBank and VIB of Vietnam International Commercial Bank, losing by 5.2-5.7%.
Only two blue chips gained: SAB of brewer Sabeco rose 3.4% and GAS of state-owned Petrovietnam Gas went up 0.6%.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, closed 2.17% lower while the UPCoM-Index for the Unlisted Public Companies Market fell 1.39%.