Roberts will leave her anchor post on Friday, August 31, reports People.
She will start preparing for her bone-marrow transplant on Monday, September 3.
In June, Roberts revealed she was diagnosed with myelodysplastic syndrome, a bone marrow disease, that she developed during her treatment for breast cancer.
Roberts will get her marrow from her sister Sally-Ann, whom she praised on her Facebook page.
She wrote: "My sister, Sally-Ann, went through a lot of tests today in preparation for being my bone marrow donor. She was such a trooper."
Roberts's team and doctors apparently will post updates on her recovery, beginning on August 31.
Watch Robin Roberts on Good Morning America below: