The index stayed in the green mostly throughout the morning, but selling pressure in the afternoon dragged it down 17 points, the largest fall since Sep. 27.
Trading value on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, shot up 28 percent to a new record of VND44.8 trillion ($1.98 billion).
The VN30 basket, comprising the 30 largest capped stocks, saw 17 tickers in the red, led by GAS of state-owned Petrovietnam Gas with a 6.9 percent drop.
The ticker is now at the lowest since Oct. 1 after plunging since earlier this month.
GVR of Vietnam Rubber Group lost 5.4 percent, hitting a four-week low.
BVH of insurance company Bao Viet Holdings also fell to a four-week low with a 4.8 percent loss.
POW of electricity producer Petrovietnam Power Corporation ended a chain of three gaining sessions with a 4.8 percent fall.
HPG of steelmaker Hoa Phat Group dropped to a 12-week low with a 3.9 percent loss. This is its fifth losing session in a row.
Eleven blue chip tickers bucked the trend, led by HDB of HDBank with a 5.9 percent gain to a new peak.
Other banks to close in the green were ACB of Asia Commercial Bank, up 2.9 percent, and VPB of private lender VPBank, 2.3 percent.
Foreign investors were net sellers for the third straight session to the tune of VND805 billion, with strongest pressure on HPG and VPB.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 3.15 percent, while the UPCoM-Index for the Unlisted Public Companies Market lost 0.25 percent.