Spanish has possessive pronouns and possessive adjectives.  An example of a possessive pronoun is mine (mío), yours (tuyo) and his or hers (suyo).

Possessive adjectives are a little bit different.  When you use the possessive adjective you include the noun in the sentence (It is my cat.  Es mi gato), and when you use the possessive pronoun you do not include the noun (It is mine.  Es mío).

Regardless of the type of pronoun, if the noun is plural the pronoun is plural.  This is much different than in English  And if you use the pronoun for "our" it must agree in gender. 

Possessive Adjectives
Singular Plural
mi(s) - my nuestro/a(s) - our
tu(s) - your su(s) - their
su(s) - his; her; its  

You may notice one problem.  "Su" or its plural "sus" can have several different meanings so you have to be careful when using it.  For example, "su car" can mean: his car, her car, its car, their car, and the same problem would exist using the plural form.  Sometimes in Spanish it would be clarified by adding the words "de él - of his", "de ella - of her" or "de ellos/ellas - of their".