The index started off in the green and gradually declined throughout the rest of the day. It closed five points lower, after gaining six points to a new peak last Friday.
Trading value on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, surged 17 percent to VND33.7 trillion, the highest since Aug. 20.
The VN30 basket, comprising the 30 largest capped stocks, was dominated by red with KDH of real estate firm Khang Dien House falling 3.9 percent from its peak.
MSN of conglomerate Masan Group lost 3.6 percent, while TPB of private TPBank fell 3.2 percent.
PDR of Phat Dat Real Estate Development continued downward with a 3 percent drop.
Seven tickers bucked the trend, with POW of electricity producer Petrovietnam Power Corporation rising 3.6 percent to the highest since April 15.
CTG of state-owned lender VietinBank gained 2.2 percent to the highest since Sep. 10.
SSI of leading brokerage SSI Securities Corporation also rose 2.2 percent to a near three-week high.
Foreign investors were net sellers to the tune of VND1.27 trillion with strongest pressure on HPG of steelmaker Hoa Phat Group and NLG of real estate developer Nam Long Investment Corp.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, gained 0.83 percent while the UPCoM-Index for the Unlisted Public Companies Market rose 0.54 percent.