Archbishop of Canterbury Rowan Williams has attended Pope Benedict XVI's inauguration in the Vatican.
Dr Williams will briefly meet Pope Benedict during his visit
His visit is being seen as a sign of good relations between the Anglican and Roman Catholic Churches.
It follows strains caused by gay marriages and the ordination of women priests by the Church of England.
Dr Williams, who will return to the UK on Monday, was expected to wear a pectoral cross presented to him by the late Pope John Paul II at the service.
During the open air mass in St Peter's Square, which is due to start at 0900 BST, Pope Benedict will receive the insignia of his office including the Fisherman's Ring, made with the image of Saint Peter, the Church's first Pope.
The leaders of the two Churches are also due to meet briefly during Dr Williams' visit.
Father Andrew Faley, assistant general secretary for ecumenism and interfaith relations for the Catholic Church of England and Wales, praised Pope Benedict XVI for expressing his desire to continue relations with the Anglican Church.
He said: "It seems as if he is going to follow in the footsteps of the previous Pope in continuing to show the pastoral care of the Catholic community towards the Anglican community."
However, he warned "theological stumbling blocks" remained.
Anglican priests have also supported Dr Rowan Williams' decision to attend the inauguration but they believe it is just the first step to resolving past differences.
BBC religious affairs correspondent Robert Pigott said that relations between the Anglican Communion and Roman Catholic Church had been strained in recent years.
This was as a result of a number of moves in the Anglican Communion - the ordination of women priests in England, the blessing of same-sex relationships and the ordination of openly gay bishop Gene Robinson in the US, he said.
When Pope Benedict was Pope John Paul II's enforcer of doctrinal orthodoxy, he issued a document that reiterated Roman Catholic primacy and questioned whether the Anglican Church was a proper church by comparison.