I came to the us in sep 2004 as au pair for 2 years. I changed my status to F1 in sep 2006. I am still currently on F1 ( I did opt from June 2009 - may 2009 ). Am I considered a resident alien or non resident alien.

Which return did you file in 2009?

I didn't file in 2009 as I did not know that I needed to file as an international student. I did opt from June 2009 - May 2010, so I filed for that last year... I used form 1040EZ.

As an au pair, you are considered to be a foreign worker. I assume you filed as a resident during at least ONE of thoese years.

When you switched over to F-1, you became a non-resident alien, and that status applied from 2006 through 2010, provided you submitted Form 8843 in each year to validate yor F-1 status. If not, the IRS will consider you to be a resident alien based on your last return filed an an au pair.