The index closed 9.2 points lower after gaining 7.9 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange, on which the index is based, rose 4.6% to VND26.41 trillion (US$1 billion).
The VN30 basket, comprising the 30 largest capped stocks, saw 24 tickers fell.
BCM of Becamex Investment and Industrial Development and LPB of Fortune Vietnam Bank both dropped 2%.
STB of Ho Chi Minh City-based lender Sacombank declined by 1.7% and BVH of insurance company Bao Viet Holdings closed 1.6% lower.
Four blue chips bucked the trend, with GAS of state-owned Petrovietnam Gas and VHM of property giant Vinhomes both rising 1.2%.
Foreign investors were net buyers to the tune of VND114 billion, mainly buying VIX of VIX Securities and MWG of electronics retail chain Mobile World.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, dropped 0.69% while the UPCoM-Index for the Unlisted Public Companies Market fell 0.31%.