Objective: The objective of this research is to develop a phonological working memory intervention program (PWMIP) and to survey its effects on increasing mean length of utterance as a language development criterion. Method: this research was conducted by single subject method. The sample includes 4 children with specific language impairment. The sample was selected after intellectual, auditory, motor tests for participation in interventional   program. The mean lengths of utterance of the sample were measured 3 times in the base line and 5 times in treatment period and changes were written down. They passed 10 sessions training.  Results: The results showed that difference in mean length of utterance before and after of training were significant. Conclusion: It is reasonable to draw a conclusion that PWMIP can be used as an effective treatment strategy to decrease language difficulties of children with specific language impairment.