Introduction: People with progressive neurological diseases such as multiple sclerosis (MS) not only experience speech production deficiencies but also language disorders. Inability in repetition of long sentences is a language difficulty. Ability in repetition of long sentence is a clinical marker of language and cognitive impairment and it can help speech and language therapists to design and implement treatment plans. Therefore, this study carried out with the aim of comparing repetition skill of long sentences in Persian-speaking MS patients and healthy people.Materials and Methods: This is a descriptive- epidemiologic study in which repetition of long sentences was carried out on 20 MS patients from the MS Society of Khuzestan (Iran). The age range of the participants was between 21-54 years (mean age 39.55) and 20 healthy people (mean age 39.50). Data includinf long sentence repetition skill, the number of errors in functional word omission, and content word omission, and number of spoken words were obtained and analyzed.Results: Results showed that there was a significant different between MS patients and the control group in the mean of long sentence repetition skill (P=0.0001), the number of errors in functional word omission (P=0.004) the number of errors in content word omission (P=0.005) and number of spoken words (P=0.001).Conclusion: Results of this study showed that repetition of long sentence skill and some of the syntactic skills have impaired in MS patients. The results can help speech and language therapists in clinical assessment and interventional programs for MS patients.