Background and Aim: Since knowing the mechanisms which evoke non-fluency is the first step in the treatment of stuttering, and there are very few researches in Persian which consider the role of the linguistic factors behind  stuttering , this study is an attempt to provide answers to some of numerous questions about stuttering by comparing  the stuttered words` type in stuttered children and adults. 
Materials and Methods: In this study stuttered people were divided into 5 age groups as follows: 3-6, 7-9, 10-12, 13-16, and older than 17 years old. Each group had ten participants. Forty-two of the 50 participants were male , and the youngest person was 3 years old and the eldest one was 32 years old. The study method involved recording at least 5 minuets of spontaneous speech of every one who was diagnosed of suffering from stuttering by two speech and language pathologists. The percent of non-fluency on every word&aposs type was determined where a content word was followed or preceded by a function word (Function-Function-Content words and Function-Content words contexts). Then these findings were analyzed by Kruskal-Wallis and Mann-Whitney tests. 
Results:  The results of this study show while function words are dominantly more stuttered than content words in children less than 13 years old in Function-Function-Content words context, we consider more disfluency on content words and second function word by getting old. We consider more stuttering on function words in children less that 13 years old in Function-Content words context too and increased non-fluency on content word by growing up. Results also show meaningful differences between the fifth group and others in the amount of stuttering on second function word in the Function-Function-Content words contexts and also between the first group and the others in amount of non-fluency both on function and content words in Function-Content words context.
Conclusion: people who stutter from Farsispeakers populations exhibit almost differential patterns of disfluency in different ages. Young speakers who stutter are predominantly disfluent on function words. There is an exchange of disfluencies from function to content words as speakers get older. Disfluencies on both function and content words are so rarely in Function-Content words and Function-Function-Content words contents. These findings support the view that stuttering on function words in children is a way of getting time to complete the next content word&aposs plan. These exchange findings are similar to what is found in English and Spanish languages and explained by the EXPLAN model.