The index stayed in the green most of the day and climbed six points at one time, but strong selling volume in the last hour of trading saw it close with a four-point drop.
Trading value on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, rose nearly 17 percent to VND22.5 trillion ($979 million). The bourse saw 200 tickers lose and 177 gain.
The VN30 basket, comprising the 30 largest capped stocks, saw 20 tickers in the red, led by STB of Ho Chi Minh City-based lender Sacombank with a 2.4 drop, ending a streak of three gaining sessions.
GVR of Vietnam Rubber Group and SSI of leading brokerage SSI Securities Corporation both dropped 1.9 percent.
VPB of private lender VPBank also lost 1.9 percent to drag VN-Index down by 0.8 point.
On the winning side, VHM of real estate giant Vinhomes rose 2 percent, while POW of electricity producer Petrovietnam Power Corporation closed 1.9 percent higher.
Foreign investors were net buyers for the six straight sessions to the tune of VND36 billion with strongest pressure on SSI and STB.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, stayed unchanged while the UPCoM-Index for the Unlisted Public Companies Market rose 0.4 percent.