Bishops, medical staff and workmen present are said to have been astonished.
An exhumation of the body of Pope John XXIII is reported to have revealed that his face is remarkably well-preserved - 37 years after his death.
According to Italian news agency ANSA, when the coffin was opened in January it was discovered that the Pope's face had not decomposed at all.
Bishops, medical staff and workmen present are said to have been astonished.
The body was exhumed in preparation for moving the former Pope's coffin from the Vatican crypts, where many popes are buried, to inside St Peter's Basilica.
Ansa quoted an official Vatican report which said Pope John looked just as he had done 37 years ago - his eyes closed, his mouth slightly open and his features immediately recognisable.
Formalin
Popes by tradition are not embalmed but John XXIII's body was treated with formalin before it was laid in state.
Born Angelo Giuseppe Roncalli, Pope John was a reforming pontiff.
He set in motion the process of modernisation in the Roman Catholic Church during his four-and-a-half year reign that ended in 1963.
He also convened the Second Vatican Council, which was a turning point in the Church's relationship with the modern world.
Popular figure
Pope John gave greater power to bishops, laid the foundations for a new relationship between Roman Catholics and Jews and ended the Latin Mass.
Known in Italy as Il Papa Buono, the kindly Pope, John XXIII has a huge following here.
The reason his body was being moved was because hoards of pilgrims quickly blocked the narrow caves under St Peter's Basilica.
He was beatified last year and the procedure for canonisation - making him a saint - is under way.