Abstrak Tujuan dari penelitian ini adalah untuk menganalisis proses berpikir siswa tunagrahita ringan dalam menyelesaikan masalah kontekstual persegi dan persegi panjang berdasarkan pemecahan masalah IDEAL. Jenis penelitian ini adalah penelitian deskriptif dengan pendekatan kualitatif. Subjek penelitian adalah 2 siswa tunagrahita ringan di SLB-C TPA Negeri 1 Branjangan. Metode pengumpulan data yang digunakan adalah tes dan wawancara. Instrumen penelitian ini yaitu peneliti, soal tes, dan pedoman wawancara. Proses berpikir kedua subjek cenderung mengalami proses disequilibrium, asimilasi, akomodasi dan equilibrium pada lima tahap IDEAL. Subjek mengalami disequilibrium ketika subjek tidak dapat memahami maksud dari soal karena belum pernah menjumpai masalah kontekstual sebelumnya, mengalami asimilasi ketika subjek menjawab pertanyaan dari peneliti secara spontan, mengalami akomodasi ketika subjek dapat menjawab pertanyaan dengan benar yang awalnya salah, dan mengalami equilibrium ketika subjek mampu memahami serta menjawab pertanyaan-pertanyaan dengan benar. Hasil penelitian ini berimplikasi bagi dunia Pendidikan khususnya sekolah yang memiliki siswa tunagrahita ringan dalam mendesain pembelajaran yang dapat memfasilitasi pemecahan masalah. Abstract The purpose of this research was to analyze the thought process of mildly retarded students in solving square and rectangular contextual problems based on IDEAL problem solving. This type of research was descriptive research with a qualitative approach. The subjects were 2 mildly retarded students at SLB-C TPA Negeri 1 Branjangan. The data collection methods used were tests and interviews. The instruments of this research were researchers, test questions, and interview guidelines. The thinking process of the two subjects tends to experience the process of disequilibrium, assimilation, accommodation and equilibrium at the five stages of IDEAL. The subject experienced disequilibrium when the subject could not understand the meaning of the problem because he had never encountered contextual problems before, experienced assimilation when the subject answered questions from the researcher spontaneously, experienced accommodation when the subject could answer questions correctly which were initially wrong, and experienced equilibrium when the subject was able to understand and answer the questions. The results of this study have implications for the world of education, especially schools with mildly retarded students in designing learning that can facilitate problem solving.