Christianity's biggest denomination opposes the ordination of women
A married teacher is poised to become Italy's first woman priest when she is ordained later this month in an Anglican church close to the Vatican.
Maria Longhitano, a member of the breakaway Old Catholic Church, says she hopes her ordination will break down "prejudice" in the Roman Church.
The event may energise the debate among Roman Catholics about the role of women, a BBC correspondent says.
Pope Benedict is implacably opposed to women as priests.
His predecessor, John Paul II, even banned official discussion of the issue, BBC religious affairs correspondent Robert Pigott notes.
While Mrs Longhitano stands to become Italy's first woman priest, women pastors are not unknown among the country's Protestants, notably the Waldensian Church.
Although Mrs Longhitano will not be a Roman Catholic priest, her ordination in the borrowed Anglican church will be acutely uncomfortable for the Vatican, he says.
When seven Roman Catholic women were unofficially ordained in 2002 they were promptly excommunicated.
Mrs Longhitano, who says she has always wanted to be a priest and played with communion wafers as a child, has accused the Vatican of preventing women from fulfilling their vocation.
She said she hoped her ordination would galvanise debate among Roman Catholics about modernisation.
Some Catholics believe reform is necessary to reverse a decline in numbers and influence and an Austrian bishop said this week that the Church should eventually consider the ordination of women.
The Old Catholics broke away from the Vatican in the 19th Century, rejecting belief in the immaculate conception and the infallibility of the Pope.
Their Church - which leaves issues such as homosexual relationships and contraception up to the individuals' consciences - has ordained women since 1996.