I'm US permanent resident can I deduct mortgage interest in mexico?

The rules for deducting mortgage interest for foreign property are the same as for property in the US:

1. The property in Mexico must be your main home or a 2nd home.
2. It either (a) isn't rented out, or (b) is rented out part time but you use the house at least 14 days/year or 10% of the number of days it's rented, whichever is longer.
3. The mortgage debt must be secured by the property itself.

If all three are true then you can deduct the mortgage interest. You can read more details in IRS Pub 936 here: Publication 936 (2011), Home Mortgage Interest Deduction (http://www.irs.gov/publications/p936/ar02.html#en_US_2011_publink1000229900)