Short answer. Only the fruits. Under Article 578 of the Civil Code, if a usufructuary brings a legal action and wins recovery of property, the usufruct is limited to the fruits of that recovered property. Dominion — ownership — remains with the naked owner, not with the usufructuary.
What the law says
If in consequence of the enforcement of the action he acquires the thing claimed, the usufruct shall be limited to the fruits, the dominion remaining with the owner.
Civil Code, Article 578 — Usufruct of a Right of Action. Read the full provision →
The usufructuary's right to sue
Article 578 of the Civil Code recognizes that a usufruct may cover a right of action — the right to sue to recover real property, a real right, or movable property. As usufructuary, you have the right to bring that action yourself, even though you do not own the underlying thing. The article further gives you the right to compel the owner to grant you authority to litigate on their behalf and to furnish you whatever proof they hold. This prevents the owner from blocking you from protecting the subject matter of the usufruct.
What you get if you win
The limitation is clear once the action succeeds. If you recover the property through the lawsuit, the usufruct shall be limited to the fruits, the dominion remaining with the owner. Winning the case does not transform your usufruct into ownership. You step into the same relationship with the recovered property that you had with the original subject of the usufruct: you enjoy the fruits, and the owner holds the dominion. The action expands what you have access to as a usufructuary — it does not elevate your right from usufruct to title.
Why this rule is consistent with how usufruct works
This outcome follows directly from the nature of usufruct. A usufructuary's right is always limited to enjoyment and fruits — never to dominion. No matter how the subject matter of the usufruct changes — whether it grows through accession, is recovered through litigation, or is expanded in scope — the usufructuary takes the benefit but not the ownership. The owner who benefits from the usufructuary's successful lawsuit is in a better position than before — the recovered property is now part of the estate — but the usufructuary's slice remains what it always was: the right to use and enjoy.
Practical implications for usufructuaries considering litigation
If you hold a usufruct that includes a right of action and are considering bringing a lawsuit to recover property, the result of winning is an expanded usufruct subject matter — not ownership. This may still be very much worth pursuing: more property in the usufruct means more fruits to collect. But you need to understand that the owner's cooperation may be required — you can demand the owner give you authority and produce their evidence, but that demand may itself require a separate legal step. Consulting a lawyer before initiating such an action will help you plan the process correctly.