Tight security surrounded St Peter's at Wednesday's service, during which the pontiff appeared on relatively good form thanks to a lighter workload over the Christmas period.
"Mary, queen of peace, bring us days of peace for the city of Rome, for Italy, for Europe and for the whole world," the 83 year-old pontiff said with marked difficulty due to the Parkinson's disease from which he suffers.
Several thousand worshippers attended the traditional Te Deum at which Rome's mayor, on behalf of Roman citizens, gave a present to the pontiff as head of the Catholic Church and Bishop of Rome.
In his homily, the pope expressed the wish that families and above all young married couples should receive encouragement and that the family should continue to "correspond to God's project".
The tight security followed a warning by Italian Prime Minister Silvio Berlusconi last Saturday that there might be a suicide attack on the Vatican on Christmas Day.
But after the pope's appearance on Wednesday, apostolic preacher Raniero Cantalamessa said on television: "Serenity wins the day in the Vatican in the face of such threats... And the pope is also a courageous man."