The index closed 5.36 points lower after gaining 1.36 points in the previous session.
Trading on the Ho Chi Minh Stock Exchange decreased by 19% to VND15.11 trillion ($615.22 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 25 tickers fell.
MWG of electronics retail chain Mobile World recorded the biggest fall with a 1.6% decline, followed by VHM of property giant Vinhomes, down 1.5%.
CTG of state-owned lender VietinBank lost 1.4% and ACB of Asia Commercial Bank dropped 1%.
Five blue chips bucked the trend, led by TCB of the largest private lender Techcombank with a 1.4% rise.
Foreign investors were net buyers to the tune of VND234 billion, mainly buying STB of Ho Chi Minh City-based lender Sacombank and VCG of Vietnam Construction and Import-Export.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 0.22%, while the UPCoM-Index for the Unlisted Public Companies Market went down 0.31%.