Short answer. Yes. Under Article 493 of the Civil Code, a co-owner may freely alienate their own part, but the effect of any alienation is limited to the portion eventually allotted to that co-owner upon partition. A buyer acquires no more than the seller actually owned, regardless of how the sale was described.
What the law says
the effect of the alienation or the mortgage, with respect to the co-owners, shall be limited to the portion which may be allotted to him in the division upon the termination of the co-ownership
Civil Code, Article 493 — What a Co-owner May Do With Their Share. Read the full provision →
What a co-owner can and cannot sell
Article 493 gives each co-owner full ownership of their part and all its fruits and benefits. They may alienate, assign, or mortgage their share freely — without needing the other co-owners' consent. But the right stops at their own share. A co-owner who purports to sell the entire co-owned property is effectively selling something that partly belongs to others. The statute is clear: the effect of the alienation, as far as the other co-owners are concerned, is "limited to the portion which may be allotted to him in the division upon the termination of the co-ownership."
What the buyer actually acquires
A buyer who purchases supposedly the whole co-owned property steps into the seller's shoes — and the seller's shoes only reach so far. The buyer becomes a co-owner together with the remaining co-owners, holding the same undivided share the seller held. The other co-owners retain their respective shares undisturbed. When partition eventually happens, the buyer receives the portion that would have gone to the seller, not the whole property. If the buyer paid for the full property believing they would get all of it, that is a dispute between the buyer and the selling co-owner — it does not bind or prejudice the non-consenting co-owners.
The same rule applies to mortgages
Article 493 expressly covers mortgages as well as outright sales. A co-owner who mortgages the whole co-owned property without the others' consent creates a lien only on their own undivided share. If the mortgage is foreclosed, the bank or creditor acquires the debtor-co-owner's share — not the entire property. The non-consenting co-owners keep their shares free of the mortgage. This protects families who co-own inherited land from having a sibling or relative secretly encumber the entire property to secure a personal loan.
Practical situation: when to assert your rights
If you discover that a co-owner sold the entire co-owned property to a third party, you do not automatically lose your share. Your share was never effectively conveyed. You can assert your continuing co-ownership by demanding partition or by challenging any attempt by the buyer to take possession of more than the seller's portion. The buyer's remedy — if they feel aggrieved — lies against the selling co-owner who misrepresented the scope of what was being sold. Understanding these limits protects you whether you are the buyer who overpaid or the co-owner whose share was sold without your knowledge.