Short answer. Yes. Under the Civil Code, if the owner of lost personal property appears and claims it, the owner must pay you one-tenth of the value of the thing found as a reward. This right is not optional — it is a legal obligation placed on the owner.
What the law says
If the owner should appear in time, he shall be obliged to pay, as a reward to the finder, one-tenth of the sum or of the price of the thing found.
Civil Code, Article 720 — The Finder's Reward. Read the full provision →
Your right to a one-tenth reward
Article 2171 of the Civil Code directs that the rights and obligations of a finder of lost personal property are governed by Articles 719 and 720. Article 720 then states plainly: if the owner appears in time, the owner is obliged to pay the finder one-tenth of the value or price of the thing found. The word "obliged" is deliberate — the owner cannot simply pocket the item back and walk away with nothing given to you. Ten percent of the item's value is your statutory entitlement for returning it honestly.
What you must do first: deposit and announcement
Your reward right depends on having fulfilled the basic duty of a finder. Article 719 requires you to return the movable to its previous possessor if you know who that is. If the possessor is unknown, you must immediately deposit the item with the mayor of the city or municipality where you found it. The mayor then publicly announces the finding for two consecutive weeks. Only after you comply with these obligations — rather than simply keeping the item for yourself — do you stand on solid ground to claim the ten-percent reward when the owner appears.
What happens if no owner appears within six months
If six months pass from the public announcement and no owner comes forward, the thing found — or its value if it was already sold at public auction — is awarded to the finder. An item that cannot be kept without deterioration, or whose upkeep would significantly reduce its value, may be sold at public auction eight days after publication, with the proceeds going to you if the owner never appears. In this scenario you get the full item or proceeds rather than a mere ten-percent reward, because no owner showed up to claim ownership.
Expenses must be reimbursed separately
The reward and the reimbursement of expenses are two separate obligations. Article 719 specifies that the finder and the owner shall each reimburse the other for expenses as the situation requires. If you incurred storage costs, transport expenses, or other reasonable outlays in preserving the item before the owner appeared, you may recover those in addition to your ten-percent reward. Document any real costs you incurred — they are a legitimate separate claim, not part of the ten-percent figure.