The men from Gauteng province were travelling to Johannesburg on Saturday night when their minibus was fired at.
The dead men, and four more who were critically injured, were returning from a colleague's funeral in the coastal region of Kwa-Zulu Natal, police said.
The motive is unclear although rivalry between groups running minibus taxi routes in South Africa has led to violence in the past.
Minibus taxis are the most popular form of transportation among South Africa's population of 55 million.
Police spokesperson Brigadier Jay Naicker said the vehicle was attacked between the towns of Colenso and Weenen, in the coastal province.
"The vehicle was ambushed. There were 11 fatalities and four were seriously injured and are in hospital," he told reporters.
"There has been a lot of taxi violence in the area but we are still investigating who the perpetrators were."
The targeted attack comes days after deadly shootings in Johannesburg, South African media reported.
In one week, a taxi owner reportedly with "no enemies" was shot dead in his vehicle, and two others were killed while travelling under a police escort.
Ten people were also killed in violence related to rivalries among minibus drivers in Cape Town over one weekend in May.