"Dear friends, the life and witness of this real disciple of Christ ... are an invitation to you and the whole church to always faithfully serve God in the poor and the needy," Benedict said as he greeted about 1,500 Missionaries of Charity gathered in St. Peter's Square for his general audience.
Mother Teresa founded the order in 1950.
"Keep following her example, and be everywhere tools of the divine mercy," the pontiff said.
Mother Teresa, a Nobel Peace Prize winner, devoted herself to helping the poorest of the poor in Calcutta, India, for about seven decades. The ethnic Albanian nun died on Sept. 5, 1997 at age 87.