The index closed 21.60 points lower after gaining 1.32 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 27% to VND29.361 trillion (US$1.15 billion).
The VN-30 basket, comprising the 30 largest capped stocks, saw 28 tickers fell.
GVR of Vietnam Rubber Group saw the biggest decline of 6.6%, followed by PLX of fuel distributor Petrolimex with a 4.0% drop.
VPB of private lender VPBank went down 3.9% and STB of Ho Chi Minh City-based lender Sacombank closed 3.4% lower.
Only two blue chips gained, including SSB of lender SeABank with a 1.4% growth and FPT of IT giant FPT Corporation, up 0.8%.
Foreign investors were net seller to the tune of VND568 billion, mainly selling FPT and VIC of private conglomerate Vingroup.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 1.77%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.99%.