Objectives: There are many reports about relations between stuttering and language development. Some studies reveal that bilingualism is a contributing factor to the development of stuttering. Main objective of this study was comparison of linguistic knowledge in Kurdish (L1) and Farsi (L2) between bilingual stutterers and their normal peers. Materials & Methods: In this case-control and comparative study all of 31 Kurdish-Farsi bilingual stutterers from 4 and 5 grades in primary schools of Javanrood were selected as case group and 31 normal peers were selected as control group by Pairs Matching Method. The linguistic knowledge of two groups in L1 and L2 were evaluated and compared by analyzing the speech quality indices (speech fluency index, speech complexity index, type-token ratio) in a sample of their spontaneous speech in Kurdish and Farsi. Data were analyzed by Independent -T-test and Mann-Whitney U. Results: In both Kordish and Farsi Language, Speech unfluency was more in stutterd students than normal group. Also, speech complexity, speech fluency and lexical diversity of stuttered students were less than normal group and there were significant differences between two groups in all speech indices (P<0.05). Conclusion: The linguistic knowledge of stuttered group was less than normal group in both Kordish and Farsi language. This finding confirms that level of language proficiency may be considered as a contributing factor to stuttering.