Sister Stanislaus Kennedy has apologised unreservedly to survivors of child abuse in Catholic-run institutions.
Sr Stan said the Sisters of Charity were sad, sorry and ashamed that children suffered physical, emotional and sexual abuse while under their care.
She also said that the order must now live up to its financial responsibilities.
Sr Stan is a prominent campaigner for homeless people.
The order is holding a conference on social justice in Dublin today.
The Ryan report into institutional child abuse the economic downturn will be discussed at the conference.
Sr Miriam Hennessey of the Sisters of Charity told the conference that the findings of the report were 'overwhelming and disturbing' for all her nuns.
On behalf of the congregation, she apologised again to all past pupils for what took place in the institutions under the congregation's care.
President Mary McAleese has described the institutional abuse of children as 'a millstone of biblical proportions in Irish history'.
Addressing a conference organised, she said the abuse of some of the children in the nuns' care was a sad chapter in their history, which calls for resilience, determination, humility and focus in the journey of amending and healing that lies ahead.