This study was carried out with 2 students with mild mental deficiency, one in 5th grade and the other in 6th grade of Turgut Özal Secondary School in Bulanik County of Mus Province. It was done during the spring semester of the 2014-2015 school year in order to observe the effect of multimedia-assisted instruction on listening skills of mainstreamed students with mild mental deficiency. The courses were taught in the information and communication technologies classroom outside the course hours with permissions from the parents and school administration. The study was designed as a case study, a qualitative research model. The lessons were videotaped to obtain data. The parents were interviewed in order to determine the state of the students after class. The data collected using semi-structured interviews was evaluated through content analysis. The study was conducted using the multimedia-assisted instruction method to discuss a total of four listening texts, with one text per week. The texts were prepared according to the multimedia-assisted instruction method. The students listened to the texts, accompanied by relevant visuals projected on a screen with background music. Tools such as animations, videos, music, etc. that reflect the central theme of the texts were prepared to be shown before and after the texts. As a result of classroom observations and interviews held with the parents, it was concluded that multimedia-assisted instruction was effective on the listening skills of mainstreamed students with mild mental deficiency. The animations, videos and cartoons that the students watched made them enjoy the lesson and become active participants in the listening process.