An internet service provider told local media Monday that cable repairs were finished on Sunday.
The fault was detected last October along the S1i branch of the AAG that connects Vietnam and Hong Kong.
Connected in November 2009, the $560-million AAG handles more than 60 percent of the country's international Internet traffic.
The cable runs more than 20,000 kilometers (12,420 miles), connecting Southeast Asia with the U.S., passing through Brunei, Hong Kong, Malaysia, the Philippines, Singapore, Thailand and Vietnam.
The other two cables, Intra Asia (IA), which broke in February, and Asia Pacific Gateway (APG) broken last December, have also been fixed.
Vietnam, where 72 percent of the population is online, has six submarine cable systems, plus a 120-gigabit channel that runs overland through China.
The APG cable, officially launched in December 2016, is capable of providing bandwidths of up to 54 Tbps (Terabit per second). It runs for around 10,400 kilometers, with connection points in mainland China, Hong Kong, Taiwan, Japan, South Korea, Malaysia, Singapore, Thailand and Vietnam.
The IA cable, which transfers data between Vietnam and Europe, North America and South America, began operations in January 2009.