Objective: Linguistic and metalinguistic knowledge are the effective factors for definitional skills. This study investigated definitional skills both content and form in children with specific language impairment.

Materials and Method: The participants were 32 Children in two groups of 16 SLI and 16 normal children, matched with age, sex and educational level. The SLI group was referred from Learning Difficulties Centers and Zarei Rehabilitation Center in Tehran, as well as the control group who was selected by randomized sampling from normal primary schools. The stimuli were 14 high frequency nouns from seven different categories. The reliability was calculated by interjudge agreement and the validity was assessed by content. Data was analyzed using independent T-test.

Results: There were significant differences between mean scores of content and form of the definitional skills in two groups. The mean and SD scores of the content of word definition were M= 45.87, SD=12.22 in control group and M=33.18, SD= 17.60 for SLI one, out of possible 70 points (P= 0.025). The mean and SD scores of the form of word definition were M= 48.87, SD= 9.49 in control group and M= 38.18, SD= 12.85 for SLI one, out of 70 points (P= 0.012).

Conclusion: Based on the results, it was concluded that, language problems of the SLI children may not let them semantic represention in order to form and present a complete process of word definition. Although this skill in children with SLI is inadequate, all the definitions given by SLI children were consistent with the categories of content and form of word definition used in this study. Therefore, an exact planning and intervention by speech and language pathologist can be effective for this skill. Linguistic intervention especially in semantic and grammatical aspects not only improves the definition of familiar words but also it might be useful for the definition of new words, consequently lead to educational and communication achievement of children with SLI.