Background: Malocclusion is the incorrect and abnormal relation between jaws and tooth. Malocclusion may cause tooth decay and periodontal diseases. The severity stages of malocclusion vary from low to high which display individual biological variation. The National Basic Health Research in 2013 reported 25,9% of Indonesian population suffered from tooth and mouth problems. The prevalence of malocclusion in Indonesia is very high, which is 80% of the total population, and it may be categorized into a very high rate oral problem. The research was conducted to discover the prevalence of tooth malocclusion on 9-11 years-old children in Islamic Primary School of Insan Utama Yogyakarta. Research Method: This research’s design is descriptive which used crosssectional research study technique. This research was performed by describing the data of tooth malocclusion’s prevalence on 9-11 years old children. There were 216 children identified as the research population and 149 children were selected as the research’s respondents based on the inclusion criteria. The research was conducted by observing teeth that suffered from malocclusion. Research Result: The research result showed that out of 149 9-11 years old children in the Islamic Primary School of Insan Utama, 82 children were categorized into class I malocclusion with 57,3% prevalence rate, 62 children were categorized into class II malocclusion with 41,6% prevalence rate, and 5 children were categorized into class III malocclusion with 3,3% prevalence rate. The malocclusion occurred to 49 boys (59,8%) and 33 girls (40,2%). The highest malocclusion prevalence rate was the class 1 malocclusion with 82 children (55,1%). Conclusion: The research of malocclusion on 9-11 years old children in Islamic Primary School of Insan Utama found that 61,7% prevalence rate occurred to boys, while the rest of 38,3% occurred to girls. The highest prevalence rate was found in class 1 malocclusion.