The index started off with a 10-point gain but gradually fell throughout the day to close with a nearly 3-point gain. It has risen in 11 of the last 12 sessions.
Trading value on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, rose 1.6 percent to VND23 trillion ($1 billion), the highest since July 12. The bourse saw 217 tickers gain and 157 lose.
But the VN30 basket, comprising the 30 largest capped stocks, was dominated by red with 17 tickers losing, led by MSN of conglomerate Masan Group with a 1.8 percent drop.
NVL of real estate developer Novaland Group lost 1.3 percent, continuing its sideways slide of the past four weeks.
KDH of real estate firm Khang Dien House lost 1.1 percent, while BVH of insurance company Bao Viet Holdings fell 0.9 percent.
On the other side, GAS of state-owned Petrovietnam Gas rose 3.2 percent to push the index up by 1.5 points.
VNM of dairy giant Vinamilk rose 1.8 percent to its highest since July 7, while PLX of fuel distributor Petrolimex continued to soar with a 1.7 percent gain.
Foreign investors recorded a net sale of VND570 billion, with strongest pressure on HPG of steelmaker Hoa Phat Group and SSI of leading brokerage SSI Securities Corporation.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, rose 1.33 percent while the UPCoM-Index for the Unlisted Public Companies Market gained 1.29 percent.