The index started off in the green but gradually declined throughout the day and closed 20.35 points lower after losing 20.55 points Thursday.
Trading on the Ho Chi Minh Stock Exchange (HoSE), on which the index is based, fell 13 percent to VND23.55 trillion ($1.03 billion).
The VN30 basket, comprising the 30 largest capped stocks, was dominated by red with FPT of IT giant FPT Corporation falling 4.2 percent after hitting a new peak.
GVR of Vietnam Rubber Group fell 4 percent and MWG of electronics retail chain Mobile World lost 3.2 percent.
Other losers included STB of Ho Chi Minh City-based lender Sacombank , down 2.8 percent, and BID of state-owned lender BIDV, down 2.7 percent.
Five blue chips gained, led by VIC of biggest private conglomerate Vingroup with a 2.8 percent increase after three sessions in the red.
VJC of budget airline Vietjet rose 1 percent after hitting the lowest in over four weeks.
Foreign investors were net sellers to the tune of VND308 billion, mainly selling VHM of real estate giant Vinhomes and STB of Ho Chi Minh City-based lender Sacombank.
The HNX-Index for stocks on the Hanoi Stock Exchange, home to mid and small caps, fell 2.17 percent while the UPCoM-Index for the Unlisted Public Companies Market lost 1.7 percent.