If chattel refers to "movable personal property," then possible antonyms are:
* Real estate
* Immovable property
* Land
* Realty
If chattel refers to "a slave or serf," then possible antonyms are:
* Free person
* Citizen
* Human being
If chattel refers to "something of value," then possible antonyms are:
* Worthless
* Valueless
* Insignificant
* Trivial
Ultimately, the best antonym for "chattel" depends on the specific context in which it's used.