Today’s lesson explains how to use leur in French. Specifically, we’ll explain leur vs. leurs as the -s can cause the meaning to change. In a nutshell, leur, leurs (possessive adjective) means “their”, leur (indirect object pronoun) means “them” and le leur, la leur, les leurs (possessive pronoun) means “theirs”. Leur comes from illorum in Latin.
leur, leurs
them, their (plural)
Pronunciation [lœʀ]

Leur vs. leurs
Example sentences
1) Possessive adjective
For this first example sentence, leur is a possessive adjective meaning “their”. Here, leur can take two forms: leur and leurs.
leur + singular noun = their + singular noun
leurs + plural noun = their + plural noun
J’aime leur chien mais je n’aime pas leurs chats.
I like their dog but I don’t like their cats.
2) Indirect object pronoun
For this second sentence, leur is an indirect object pronoun meaning “them”. For this usage, adding an -s would be wrong. There is one form: leur. This is a common mistake among students.
Verb: Téléphoner à quelqu’un= to telephone/call somebody
Je leur téléphone = I call them (present tense)
Je leur ai téléphoné = I called them (passé composé)
Je leur ai téléphoné mais ils n’ont pas répondu.
I answered them but they didn’t reply.
3) Possessive pronoun
For this final sentence, le leur means “theirs”. This is a possessive pronoun (mine, yours, etc.) There are three forms for leur in this instance:
le leur = theirs (for masculine noun)
la leur = theirs (for feminine noun)
les leurs = theirs (for plural noun)
J’aime mon cheval mais je préfère le leur.
I like my horse but I prefer theirs.