The index started off in the green but plunged in the afternoon and closed almost 22 points lower after losing nearly one point Friday.
Trading on the Ho Chi Minh Stock Exchange (HoSE) increased by 7 percent to VND13.33 trillion ($579.56 million).
The VN-30 basket, comprising the 30 largest capped stocks, saw 27 tickers dropped.
SSI dropped 6.85 percent, continuing to fluctuate around its one-year low level.
It was followed by five banks, with STB of Ho Chi Minh City-based lender Sacombank losing 5.8 percent TPB of private TPBank falling 4.5 percent.
Other losers included MSN of conglomerate Masan Group, VNM of dairy giant Vinamilk and HPG of steelmaker Hoa Phat Group.
BVH of insurance company Bao Viet Holdings was the only ticker that bucked the trend by rising 1.2 percent.
Foreign investors were net sellers for the third straight session to the tune of VND439.11 billion, mainly selling SSI and VIC of biggest private conglomerate Vingroup.
The HNX-Index at the Hanoi Stock Exchange, where mid and small caps list, was down 2.07 percent while the UPCoM-Index at the Unlisted Public Companies Market was down 0.51 percent.