Wildlife protection is complicated in Congo by lawlessness and militia violence that endures 15 years after the end of a war that killed millions, mainly from hunger and disease.
"The Zimbabwean Government was satisfied that the pre and post-translocation conditions in [Congo] met the requisite standards for a successful re-establishment of rhinos," a ZimParks statement said.
ZimParks and conservationists said moving the rhinos from Zimbabwe would strengthen the gene pool. Zimbabwe had about 800 black and white rhinos in 2016 and is one of just four countries with nearly all the world's white rhinos.
Their horns are prized in China and southeast Asia.
"Moving rhinos from one place to another is essential to ensure good genetic diversity across the population," said Emma Pereira, a spokeswoman for Save the Rhino, a London-based group. "We hope any move between countries is done with the correct expertise and thoughtful planning."