Mi, tu, su in Spanish: possessive adjectives

Mi means “my”, tu means “your” and su means “his”, “her”, “your” (formal) or “their”. The key rule is that these words agree with the thing owned, not the owner, and they change for number only: singular mi, tu, su become plural mis, tus, sus.

Agree with what is owned, in number

Look at the noun after the possessive, not at who owns it. One book takes the singular form; several books take the plural.

mi libro, mis libros
my book, my books

tu amiga, tus amigas
your friend, your friends

This is why mi never becomes mía here: it changes for number, not gender.

Su covers four owners

Su and sus can mean his, her, your (formal usted) or their. Context usually makes it clear.

su casa
his / her / your / their house

sus hijos
his / her / your / their children

Use “de + person” when su is unclear

When su is genuinely ambiguous, Spanish often replaces it with de plus the owner to be precise.

el coche de ella
her car

la oficina de usted
your office

Nuestro also agrees in gender

The “our” form is different: nuestro changes for both gender and number, giving nuestro, nuestra, nuestros, nuestras.

nuestra casa, nuestros amigos
our house, our friends

Common mistakes

Matching the possessive to the owner

A man’s books are still sus libros, not su libros; the form follows the plural noun.

su libros → sus libros
his books

Confusing tu and tú

The possessive tu (your) has no accent; tú with an accent means “you”.

tú casa → tu casa
your house

Adding gender to mi and tu

Mi and tu never become mía or tua as adjectives before the noun; only number matters.

mía hermana → mi hermana
my sister

Possessives lean on the same number agreement you practice with the Spanish plural rules, and the de fix here is the same preposition you sort out in de vs del. In Fluera these small words appear inside family and home sentences, so you choose mi, tu or su from a real context. Use that when you practice Spanish and the agreement starts to feel natural.

Practice