Sisters of Mercy Judith Redden, 71, who retires as principal of Adelaide's St Aloysius College in two weeks, is aware there are few women taking their vows and even fewer nuns in schools.
"If I talk about this school, in the next 10 years there probably won't be any sisters left," Sister Judith said.
Catholic Religious Australia surveys show the number of nuns has decreased by 63 per cent since the mid-1970s, and almost 70 per cent since their peak in the mid-60s.
The lack of women training to become nuns has posed problems, with orders considering national instead of local convent-based education for as few as one candidate annually.
There were 4765 nuns in Australia last year compared with 12,619 in 1976 and a peak of 14,622 in 1966. In 1901, there were 3622.
Between 1997 and 2008, only 206 women became nuns, and 42 of those resigned by 2009.
An average of 160 nuns died in each of those years.
Their current median age is 74 and 94 per cent are aged over 50.