The following table shows the possessive pronouns in Spanish.

mine	mío
yours	tuyo
his, her, its, yours	suyo
ours	nuestro
yours	vuestro
theirs, yours	suyo

The possessive pronouns change their number and gender together with the thing that is possessed. They do not change their number and gender together with the possessor.

Your hair is short. Mine is longer than yours.	Tu cabello es corto. El mío es más largo que el tuyo.
The words are his. They are not mine.	Las palabras son suyas. No son mías.
What is ours is yours.	Lo nuestro es vuestro.
The dogs are theirs.	Las perras son suyas.

Since suyo can refer to many different persons, you can disambiguate it by using de + person instead.

The book is hers.

El libro es de ella.

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