Objectives: Grammar is frequently considered as the strength in the language profile of autistic children. Only a few studies have investigated the grammatical knowledge of these children. There are some research studies, but they are inconclusive, and less is known about the linguistic characteristics of children with autism in some languages, like Persian. Thus, the present study aimed at the detailed examining of syntax comprehension in Persian speaking children. 
Methods: The required data were collected from 10 children with autism (6-9 years old) and 20 healthy children (10 age-matched and 10 language-matched). Then, we used the Gilliam autism rating scale (GARS-2) for diagnosing autistic children. We used syntax comprehension test for assessing syntactic structures in children with autism and their normal peers. The obtained data were analyzed by statistical tests.  
Results: The obtained results suggested a significant difference between the autistic group and age-matched healthy group in all structures, except for two elements, negative, an irreversible three-element sentence, reversible above and below, as well as sentences with object and subject pronoun. However, a comparison between the autistic group and the language-matched group revealed no significant difference in most structures, except for reversible passive, relative clause in the subject, relative clause in the object, and singular/ plural infection.
Discussion: Overall, autistic children have consistent comprehension impairment in relative clauses, reversible sentences, and morphosyntax, which should be seriously treated. The comparison of children with autism with age-matched healthy children indicated that a syntax comprehension test could be useful for differentiating Persian speaking children with autism from those with simple language delays.