Sister Mary Kreuper and Sister Lana Chang took the funds from St James' Catholic School in Torrance, near Los Angeles during a number of years.
Their order, the Sisters of St Joseph of Carondelet, said: "The Sisters have confirmed the misappropriation of funds and have cooperated in the investigation.
"Our community is concerned and saddened by this situation and regret any injury to our long relationship with the families of the school."
The convent said it had been alerted by the Archdiocese of Los Angeles of an investigation into the finances of the school, where a "diversion of funds" was detected.
The pair, who have each recently retired and were described as best friends, withdrew the cash from an account which handled donations and tuition fees at St James Catholic School.
It is claimed they were able to disguise their actions by depositing numerous cheques made out to the school into another bank account.
In a letter written to parishioners and seen by the AFP news agency, the monsignor of St James Catholic Church, Michael Meyers said both women have expressed "deep remorse" and asked for forgiveness.
Church leaders do not plan to press charges.
Stay up to date with the latest news stories from a Christian perspective. Sign up to our daily newsletter and receive more stories like this straight to your inbox every morning.