British model Naomi Campbell will give evidence about a "blood diamond" she was allegedly given by Taylor during a party hosted by then-South African President Nelson Mandela in 1997.
Her spokesperson said Campbell "is not being accused of any wrongdoing and is not on trial."
Elyse Kepler, a Sierra Leone special courts expert and lawyer with Human Rights Watch in New York, told RFI that Campbell had originally refused to talk to prosecutors - until she was warned by Sierra Leone's Special Court she could face up to seven years in jail for keeping mum.
"What I understand is that the prosection's case is being reopened as she is now available and coming to testify," Kepler said.
Taylor has been on trial since 2008, charged with arming Sierra Leone's Revolutionary United Front in a brutal civil war that is thought to have killed 120,000 people.
Taylor's gift to Campbell was allegedly one of the gems he had received from the Sierra Leone rebels and then taken to South Africa to sell or exchange for weapons.
He has pled not guilty to charges including murder, rape, conscripting child soldiers, enslavement and pillaging.