The 'Taiping Four' gorillas will be back in Cameroon on Friday, the National Zoological Gardens of SA and the International Fund for Animal Welfare said on Wednesday.
"The full repatriation team has gathered and is on standby," they said in a joint statement. The gorillas would board a plane late on Thursday and arrive back in Cameroon early on Friday.
The western lowland gorillas were sent to the Pretoria Zoo in 2004 at the request of Malaysia, which confiscated them in 2002 after discovering they had been illegally imported to its Taiping Zoo from Nigeria.
Cameroon asked that the animals be returned to their country of origin. The three females and a male are known as Izan, Abbey, Tinu and Oyin, and are aged between six and nine.
Trade in endangered species and violation of the Convention on the International Trade in Endangered Species (CITES) was fast leading to the extinction of entire species, said Ifaw spokeswoman Christina Pretorius.
"The IUCN Red List recently moved the status of Western Lowland gorillas from endangered to critically endangered, largely as a result of being hunted, killed and captured for commercial use," she said.
The gorillas were to have been repatriated in December last year, but their return was put on hold in the absence of SA's formal consent to the relocation.
At the time, the government committed itself to ensuring the animals' safe return, and pledged to expedite the process.
Their relocation follows years of lobbying by, among others, the Born Free Foundation, the Pan African Sanctuary Alliance, the International Primates Protection League, and the Last Great Ape Organisation.
This amid arguments that the gorillas would be safer in SA, where they would be protected from poachers who might hunt them for meat. The Pretoria Zoo accommodated them in specially-constructed habitats.
Pretorius said on Wednesday that the gorillas would be sent to the Limbe Wildlife Centre sanctuary.
She said Limbe staff had spent the past two weeks at the Pretoria Zoo preparing the animals for departure. The zoo was sending two primate keepers to Cameroon with them to help them settle in.
"We don't anticipate any hitches in the coming few days and our veterinary team of experts and gorilla keepers are confident that our work will realise a seamless return for the gorillas to Cameroon," said the National Zoological Gardens of SA's executive director Dr Clifford Nxomani.
The animals will leave SA on board a scheduled Kenya Airways flight from Johannesburg, via Nairobi and on to Douala in Cameroon.