Siswa tunagrahita ringan kelas II di SDLB mengalami kesulitan untuk memahami konsep geometri terutama bangun datar. Media slime merupakan alternatif penyelesaian dari masalah tersebut. Tujuan penelitian adalah (1) mendeskripsikan pemahaman konsep geometri siswa tunagrahita ringan sebelum diberi perlakuan menggunakan media slime, (2) Mendeskripsikan pemahaman konsep geometri siswa tunagrahita ringan kelas II SDLB setelah diberi perlakuan menggunakan media slime dan (3) Mendeskripsikan pengaruh media slime terhadap pemahaman konsep geometri siswa tunagrahita ringan kelas II SDLB.. Jenis penelitian adalah eksperimen kuasi dengan desain one group pretest-posttest. Data akan dianalisis menggunakan analisis deskriptif dan uji hipotesis menggunakan uji wilcoxon. Hasil penelitian ini menunjukan (1) Pemahaman konsep geometri siswa tunagrahita ringan kelas II SDLB sebelum diberikan treatment mendapatkan nilai rata-rata 48.8 yang dikategorikan kurang. (2) Pemahaman konsep geometri tunagrahita ringan kelas II SDLB sesudah diberikan treatmen memperoleh nilai rata-rata 76.8 yang dikategorikan baik. (3) Hasil uji wilcoxon yang diperoleh Thitung = 0, jika dibandingkan dengan Ttabel maka Thitung (0) < Ttabel (1). Hasil tersebut menunjukan bahawa Ho ditolak. Kesimpulan dari penelitian ini adalah terdapat pengaruh media slime terhadap konsep geometri siswa tunagrahita riingan kelas II SDLB.Students with mild intellectual disability in 2nd grade sdlb find it difficult to understanding the concept of geometry especially shapes flat. As an alternative the completion of the issue was slime media. The purposes this research are ( 1 ) described understanding the geometry concept of students with mild intellectual disability in 2nd grade SDLB before given treatment uses the media slime, ( 2 ) described understanding the geometry concept of students with mild intellectual disability in 2nd grade SDLB after he received treatment uses the media slime and ( 3 ) described the influence of media slime to understanding the geometry concept of students mild intellectual disability in 2nd grade sdlb .The kind of research is quasi experiment with the design one group pretest-posttest.The data collected will be analyzed use descriptive analyzed and the hypothesis use wilcoxon test.The result of this research showed 1) understanding of the geometry concept of the mild intellectual disability students class II treatment given before SDLB gets an average of 48.8 categorized less. (2) Understanding the geometry concept of mild intellectual disability class II SDLB after given treatmen gained an average rating of 76.8 categorized either. (3) the wilcoxon test results obtained Thitung = 0, when compared to the Ttabel then Thitung < Ttabel (0<1). By comparison like that then Ho denied and Ha is received. The conclusion from this study is there is influence slime media against the concept of geometry students mild intellectual disability class II SDLB.