The index closed 13.31 points lower after gaining 3.12 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 9% to VND15.229 trillion ($622.33 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 24 tickers fell.
SSI of leading brokerage SSI Securities Corporation dropped 4.3%, followed by STB of Ho Chi Minh City-based lender Sacombank with a 4.1% decline.
HPG of steelmaker Hoa Phat Group and VHM of property giant Vinhomes both dropped 2.9%.
Six blue chips gained, led by VPB of private lender VPBank with a 2.5% rise.
Foreign investors were net seller to the tune of VND826 billion, mainly selling MWG of electronics retail chain Mobile World and FPT of IT giant FPT Corporation.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, dropped 1.08% while the UPCoM-Index for the Unlisted Public Companies Market fell 0.63%.