The index closed 24.55 points lower after gaining 6.45 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange increased by 22% to VND21.40 trillion ($848 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 28 tickers fell.
BCM of Becamex Investment and Industrial Development plunged the steepest with a 7% decline.
GVR of Vietnam Rubber Group lost 4.8% and SSI of brokerage SSI Securities Corporation fell 4.7%.
MBB of lender MB lost 4.1% and STB of Ho Chi Minh City-based lender Sacombank closed 3.3% lower.
Two blue chips bucked the trend. VCB of state-owned lender Vietcombank rose 1.7% and SSB of SeABank increased 0.7%.
Foreign investors were net buyers to the tune of VND61 billion, mainly buying VCB and VNM of dairy giant Vinamilk.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 2.61%, while the UPCoM-Index for the Unlisted Public Companies Market went down 1.63%.