Back ground and aim: Specific language impairment is one of developmental language disorders in children which have no known etiology. Very few researches have been done about children with this type of disorder in Persian language. The aim of this study is to detect whether there are similarity in language abilities between SLI children and their MLU -m matched group or not.

 Materials and Methods: In this case- control study, the results of speech samples analysis, quotients for composite scores and standard scores of subtests of TOLD, from 12(7 boys and 5 girls) 5-7 years old children with SLI were compared with the results obtained from 12 younger normal (8 boys and 5 girls) children who were matched according to MLU- m with SLI children.

 Results: results show that there are no obvious differences in percent- point average use of words and morphemes in speech between two groups. While the two groups were adapted according to m-MLU, but we found that children with SLI are significantly lower than their MLU matched children in quotients for composite scores of spoken language, organization and semantic and in standard scores of sentence imitation, relational vocabulary and oral vocabulary subtests of TOLD.

Conclusion: Our findings demonstrated that some language skills in children with SLI are lower than their MLU matched peers. Results of this study were not provided evidence to support the hypothesis that children with similar m-MLU have similar language skills too. So it is necessary for clinician to consider it when they work with these children.