In this study, we have examined the effectiveness of operant conditioning on the development of linguistic skills in Persian children with autism. It was a quasiexperimental study, and done by using pre-and post-tests. We randomly selected 40 children (6 girls and 34 boys, 5-10 years old) and divided them into experimental and control groups comprising of 20 children each. We used the Autism Spectrum Screening Questionnaire (ASSQ) to screen subjects and the Test of Language Development (TOLDP: 3) to measure their language skills. Both groups received grammatical comprehension and grammatical completion subtests. Using the Applied Behavior Analysis (ABA) method, the experimental group was then subjected to 48 one-hour intervention sessions ran for 24 weeks. After the intervention, we ran a post-test in both experimental and control groups. The data were analyzed using SPSS software. In the experimental group, the mean score in the grammatical completion subtest had increased by 4. 2, and in the grammatical comprehension subset, the mean score had increased by 3. 6. In contrast, in the control group, the mean score of the grammatical completion and comprehension subtests had increased by 0. 25 and 0. 3, respectively. The findings suggested that operant conditioning had direct effects on the improvement of the 5-10 years old Persianspeaking children with autism.