This research investigated the word reading performance of Persian speaking dyslexic children through the use of a reading test. For this reason, 15 Persian elementary developmental dyslexic student with the mean age of 9.6, (SD= 1.5) and 15 Persian unimpaired elementary student with the mean age of 9.6 (SD= 1.4) were compared. The performance of the two groups was examined according to the effect of transparency variable. Participants were required to read a list of 32 one syllabic word and nonwords in order to compare the reaction times and error rates of reading transparent and opaque words and nonwords. Overall, the finding showed that dyslexic children encountered more problems in reading both transparent and opaque words than did unimpaired children. The finding also showed that reading the opaque words was harder than reading the transparent words for both groups. The results of this research show that specific charactristics of writing systems affect the word processing ability of individuals in the reading task.