The world's first double leg transplant will happen once a donor is found, Spain's health ministry has announced.
A man who lost his legs in an accident, and who cannot use prosthetic limbs, will be the recipient.
A double-arm transplant was carried out in Munich in 2008, but no-one has yet received a leg transplant.
The doctor leading the leg transplant team, Pedro Cavadas, performed Spain's first double-hand transplant in 2006.
That operation took place at the Hospital de la Fe in Valencia, where the leg transplant will also be carried out.
The announcement was made at an international conference in Madrid, called the "Last frontiers of transplant operations".
The leg operation was approved in May by the ministry's transplant commission.
Spain's health minister, Leire Pajin, also announced the approval of Spain's fourth face transplant at the conference.
This operation will also be carried out by Dr Cavadas, who is hailed in the Spanish media as a "miracle doctor".
The world's first full facial transplant was carried out in Spain earlier this year by a different surgeon, Joan Pere Barret.
"Transplants of hands, arms or faces from dead people were science fiction just a decade ago and today they are a splendid reality at our hospitals," said the director of Spain's National Organisation of Transplants, Rafael Matesanz, at the opening of the conference.
A spokeswoman quoted by the Agence France Press news agency said the leg transplant operation could take place in two or six months, depending on when a suitable donor was found.