Short answer. It stays yours. In a universal partnership of profits, the movable or immovable property each partner owned when the contract was made continues to pertain exclusively to that partner — only the usufruct, the right to its fruits and use, passes to the partnership. What the partnership shares is what the partners acquire by their industry during its existence.
What the law says
Movable or immovable property which each of the partners may possess at the time of the celebration of the contract shall continue to pertain exclusively to each, only the usufruct passing to the partnership.
Civil Code, Article 1780 — Universal Partnership of Profits. Read the full provision →
Ownership stays with the partner
Article 1780 answers the question directly for the property you already own. Movable or immovable property which each of the partners may possess at the time of the celebration of the contract shall continue to pertain exclusively to each, only the usufruct passing to the partnership. So your house, your land, your car — whatever you owned when the partnership was formed — remains yours. Ownership is not transferred into a common fund the way it is in a partnership of all present property. This is the defining difference between the two universal partnerships: one pools existing wealth, the other leaves each partner the owner of what he brought.
But the usufruct passes to the partnership
What the partnership does get is the usufruct of that property — the right to use it and to enjoy its fruits — even though the bare ownership stays with the partner. So if you own an apartment and bring it into a universal partnership of profits, you remain its owner, but the rents it produces during the partnership belong to the partnership, not to you alone. The land is yours; its harvest is the firm's while the partnership lasts. This split between naked ownership and usufruct is the mechanism the article uses to share the benefit of a partner's existing assets without ever taking away the assets themselves.
What the partners actually share
On the profit side, the article says the partnership comprises all that the partners may acquire by their industry or work during the existence of the partnership. So the shared pool is built from what the partners earn through their effort while the partnership runs — the fruits of their labour and skill — together with the fruits of the property whose usufruct they contributed. What the partners owned before, and what comes to them during the partnership by a route other than their industry is not automatically caught, because the sharing is of earnings from work, not of every asset a partner touches.
Why the distinction matters
For anyone forming a universal partnership, this is the setting that keeps your patrimony intact. You do not give up ownership of what you have built; you lend its use and share what you earn going forward. When you draw up the agreement, be explicit that it is a partnership of profits if that is what you intend, list the property whose usufruct is contributed, and record who owns what, so that when the partnership ends each partner simply takes back his own property.