Prepositions represent an evident problem for children diagnosed with Specific Language Impairment (SLI), as they tend to elide prepositions or incorrectly use them in their oral production. This subject has been described in different languages, in Spanish it has not been studied in depth. In this context, the present work seeks to describe and analyze, qualitatively, the errors in the use of prepositions in Chilean children diagnosed with SLI. For this, oral narratives were analyzed produced by 38 children starting preschool between 5 and 5 and 11 month of age, and diagnosed with SLI. Narratives were elided through recounting and were phonetically transcribed. Thereafter, contexts where prepositions appeared were analyzed and it was determined if they matched with adequate use, elisions, or particle substitutions. Data indicate that there are three grammatical factors which seem to influence in the production of grammatical deviations in contributions that incorporate prepositions: (i) the functional nature of prepositions, (ii) the obligatory nature of the components, and (iii) the incongruence between the thematic roles and syntactic functions.