Background and Aim: Hearing impairment can effect many educational abilities and will lead in a dealy in his growth. The objective of this research was to study the effect of hearing impairment on mathematical skill of hearing-impaired students of 4th grade of elementary in contrast with normal-hearing students.Methods: The project was cross-sectional and the tool used was the international standard booklet of mathematical questions. There has been 35 hearing-impaired students with range of moderately sever-profound hearing loss selected from the 4th grade of elementary from exceptional schools in Ray, Pakdasht and Varamina, Iran, and 35 normal-hearing students were randomly selected from ordinary schools next to exceptional schools.Results: By analyzing the outcomes, the normal-hearing students showed a better result in knowing, application, argument in aspects of cognitive in contrast with hearing-impaired students and there has been a meaningful difference (p<0.05). There was not a meaningful difference in mathematical skill between Ray, Pakdasht and Varamina, Iran in hearing-impaired and normal-hearing groups.Conclusion: The hearing impairment effects learing of mathematical skill. It is important for hearing-impaired students to presentation various methods in instruction in progress deductive thought and cognitive structure and also development in concepts understand in mathematical domain in rehabilitation services.