Short answer. No. The usufructuary of a mortgaged immovable is not obliged to pay the debt the mortgage secures. If the property is attached or sold judicially to satisfy that debt, the owner must answer to the usufructuary for whatever he loses because of it.
What the law says
The usufructuary of a mortgaged immovable shall not be obliged to pay the debt for the security of which the mortgage was constituted.
Civil Code, Article 600 — Mortgaged Property in Usufruct. Read the full provision →
The debt belongs to the person who borrowed
A mortgage does two things at once, and the article separates them. It creates a personal obligation to repay, which stays with whoever borrowed the money, and it charges the property as security, which follows the property. The usufructuary took the enjoyment; he did not take the loan. So the lender's demand for payment is not his to answer, and he does not become a debtor merely because the thing he enjoys happens to stand as collateral. That is true however plainly the encumbrance appears on the title he was shown.
What the exemption does not protect him from
Being free of the debt is not the same as being safe from the mortgage. The charge on the property survives the usufruct and can be enforced against it, which is why the article goes straight on to contemplate the immovable being attached or sold judicially for the payment of the debt. If that happens, the usufructuary's enjoyment can be cut short by a proceeding he was never party to and had no power to prevent. He is not liable, but he is exposed — a distinction that matters greatly to anyone deciding whether to accept a usufruct over encumbered property.
The owner has to make him whole
That is what the second sentence is for. Where the property is taken to satisfy the debt, the owner shall be liable to the usufructuary for whatever the latter may lose by reason thereof. The claim is against the owner personally, not against the buyer at the sale or the lender, and it is measured by the usufructuary's loss — the enjoyment he was entitled to and no longer has. The practical consequence is that a usufructuary's protection is only as good as the owner's ability to pay, which is a poor consolation where the owner has just been sold up.
What to check before accepting the usufruct
The certificate of title is the document to ask for, and it should be read for what is annotated on it as much as for whose name is on the front: existing mortgages, their amounts, and any notice of an adverse claim or pending action. If a mortgage is there, find out who the debtor is and whether the loan is current, because the risk to the usufruct is the risk of default. Where the usufruct is being created by deed, this is also the moment to negotiate expressly for what happens if the mortgage is enforced.