This thesis proposes that, once understood that the social labor of the librarian is in narrow relation with the education, then he can take an active role in sexual education during elementary school. Since the principal tool of every librarian to realize his educational labor is the library collection and specially children books, then it will be its major tool to fullfil it. Even though the librarian is not a teacher, he must be qualified to find the information the users require, and in coordination with other professionals of the educational system it can select and acquire the collection that answers to the information needs. In addition, she or he is able to handle any type of information in any format, he possesses the elements to find the information, therefore, he can give the children the materials and the information that they need. This work presents the different ways in which the school librarian can interfere and fulfill his sex educational role not only at the moment to select and acquire the library materials, but also at the librarian services and the activities of reading promotion in the library.