Despite being born in Israel, the 29-year-old actress says her No Strings Attached co-star has taught her a lot about her faith.
The recent Golden Globe winner tells USA Today: 'Ashton has taught me more about Judaism than I think I have ever learned from anyone else.
'Ashton's a very serious student of Kabbalah and Judaism. He knows a lot.
'When we had the funeral scene [in No Strings Attached], that was a Jewish funeral.
'He was able to read all the Hebrew. It's very impressive.'
Along with his wife, Demi Moore, 32-year-old Kutcher is a Kabbalah devotee.
He was a little bashful when responding to Portman's claims, saying: 'I can make the noises. I don't know what they mean.
But the actress tells the newspaper: 'No, you like - he reads the Torah every Saturday.'
Worried that she has revealed too much, the pregnant actress quickly says: 'I hope this isn't too private to reveal, but it's very impressive.'