Here are some options depending on the context:
If "property" means possessions or belongings:
* Nothingness
* Lack
* Absence
* Emptiness
If "property" means a piece of land or real estate:
* Common (as in land not privately owned)
* Public
* Unclaimed
If "property" refers to a characteristic or quality:
* Flaw
* Defect
* Shortcoming
* Liability
If "property" means a mathematical or physical attribute:
* N/A (since this meaning doesn't have a direct opposite)
To give you a better antonym, please provide the specific context in which you're using the word "property".