It was found in a preliminary study conducted on mild mentally retarded children aged 9-12 years at SLB Tunas Mulya Surabaya, most of them had poor knowledge of how to brush their teeth. This is caused by the use of media that is less effective in the learning process. Efforts to increase knowledge of dental and oral health maintenance can be carried out by using MEDBOGI (Media Boneka Gigi). This study aimed to determine the effect of using MEDBOGI on knowledge of how to brush teeth in children with mild mental retardation at SLB Tunas Mulya Surabaya. The research method uses analytic research with quick experimental and one-group pretest-posttest design. The research sample was 30 mentally retarded children aged 9-12 years at SLB Tunas Mulya Surabaya, taking samples using a total sampling technique. The data collection instrument uses a questionnaire sheet. The data analysis technique uses the Mann-Whitney test. Results: based on the Man-Whitney test, the result is P (0.000) <0.05. This value indicates that H0 is rejected, so there is an effect of using MEDBOGI on knowledge of how to brush teeth in children with mild mental retardation at SLB Tunas Mulya Surabaya.