The index closed 0.02 points lower after gaining 5 points Tuesday.
Trading value on the Ho Chi Minh Stock Exchange rose 6.9% to VND22.59 trillion ($920.80 million).
The VN30 basket, comprising the 30 largest capped stocks, saw 17 tickers dropped.
VIC of private conglomerate Vingroup fell 2.6%, followed by VHM of property giant Vinhomes, down 2.5%.
MWG of electronics retail chain Mobile World dropped 1.5% and HPG of steelmaker Hoa Phat Group closed 1.4% lower.
Thirteen blue chips gained.
TPB of private TPBank rose 4% and BCM of Becamex Investment and Industrial Development closed 3.1% higher.
Foreign investors were net buyers to the tune of VND23 billion, mainly buying MSB of Vietnam Maritime Commercial Bank and STB of Ho Chi Minh City-based lender Sacombank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, gained 0.15% while the UPCoM-Index for the Unlisted Public Companies Market rose 0.09%.