Figures released yesterday by the Church show that 40,224 Austrians left the Church last year - up from 36,293 in the previous year.
Erich Leitenberger, the Vienna archdioceses press spokesman, added though that the number of people returning to the Church increased from 4,262 in 2007 to 5,037 in 2008.
He said the number of Catholics involved in helping prepare people for First Communions and Confirmations had increased from 2007 to 2008.
He also said the reported number of Catholics didnt take into account what he called the "underground" Church. He said: "There are many Catholic immigrants who come from countries where it was not advisable and in many cases still isn't advisable publicly to profess the faith."
Leitenberger added that Church attendance on Sundays had averaged 729,879 in 2008, down from 779,418 in 2007. He said many "cultural Catholics" went to Church only once a month or on the main feast days of the liturgical year.
Austria has the eighth highest percentage of people claiming to follow a religious faith - 79 per cent - among European Union (EU) member states, according to EU statistics.