The aim of this research is to study according to which criteria intellectual deficient children categorize exemplars belonging to the world of living and not living, compared with typically developing children of the same mental age. In order to do that, we used a free-sorting task which gives the possibility to differentiate organizational and functional aspects of categorization activity. In the first step, we asked children to sort out pictures spontaneously. During the second step, three heaps must be constructed which correspond to the three ontological categories manipulated by our experience (animals, plants and artefacts) and in the third step, two heaps must be done corresponding to categories of living and not living. Our results show that taxonomic and thematic categories coexist and are similarly organized for the intellectual deficient children and the typical children matched by mental age and their evocation depends of subject experience and the complexity of the task. Similarly, the use of these categories is similar for our two populations for the animals and plants and different for artefacts. On the other hand, when the task gets harder (step 2 and 3) and its resolution needs a change of strategy, the intellectual deficient children have performances inferior to the typically developing children.