The index closed 2.5 points lower after gaining 19.4 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange fell 9.42% to VND17.31 trillion (US$661.2 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 15 tickers dropped.
VIC of private conglomerate Vingroup lost 2.55%, PLX of fuel distributor Petrolimex went down 1.54%, and BVH of insurance company Bao Viet Holdings saw a 1.43% decline.
Eight blue chips gained. LPB of Fortune Vietnam Bank was up 4.39%, FPT of tech giant FPT Corporation rose 1.49%, and SAB of brewer Sabeco closed 0.93% higher.
Foreign investors were net sller to the tune of VND88 billion, mainly selling VCB of state-owned lender Vietcombank and VHM of property giant Vinhomes.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, slipped by 0.74%, while the UPCoM-Index for the Unlisted Public Companies Market went up 0.45%.