AbstrakPenelitian ini bertujuan untuk mengetahui (1) jenis-jenis kesulitan belajar matematika materi keliling dan luas bangun datar, (2) untuk mengetahui faktor-faktor penyebab kesulitan belajar matematika materi keliling dan luas bangun datar siswa kelas III SD Brajan Tamantirto Kasihan Bantul. Penelitian ini adalah penelitian deskriptif kualitatif. Populasi dalam penelitian ini sebanyak 26 siswa dengan sampel sebanyak 8 siswa dan menggunakan teknik pengambilan sampel yaitu purposive sampling. Pengumpulan data dilakukan melalui triangulasi teknik. Triangulasi teknik dalam penelitian ini meliputi observasi, wawancara dan kajian dokumen. Triangulasi teknik digunakan untuk mendiagnosa kesulitan belajar matematik yang dialami oleh siswa melalui beberapa tahapan diagnosa yang ada. Teknik analisis data yang digunakan dengan model Miles and Huberman terdiri dari: reduksi data, paparan data, dan penarikan kesimpulan. Hasil penelitian ini menunjukkan kesulitan belajar matematika materi keliling dan luas bangun datar yang dialami oleh siswa meliputi: tidak mengerti konsep rumus dengan persentase sebesar 38,5%; kekeliruan dalam operasi perkalian dengan persentase 34,6%; kekeliruan dalam operasi pembagian dengan persentase 16,7%; dan kekeliruan dalam membaca dan mengerti soal cerita dengan persentase 38,4%. Faktor yang menjadi penyebab kesulitan belajar matematika diantaranya: faktor psikologis siswa yang tidak menyukai mata pelajaran matematika, faktor guru yang kurang menguasai materi pelajaran, dan kurangnya keharmonisan keluarga terkait interaksi siswa dengan anggota keluarga lain.Kata kunci: Kesulitan Belajar MatematikaAbstractThe aims of the research were to know (1) the kinds of difficulty in mathematics study about circumference and wide of two-dimentional figure, (2) the factors that caused why students got difficulty in mathematics study at circumference and wide of two-dimentional figure materials in the 3rd grade students at Brajan Elementary School of Tamantirto Kasihan Bantul. The research was descriptive qualitative research. The population in this research were 26 students with the sample were 8 students and used sampling technique was purposive sampling. The data collection technique was conducted by triangulation technique. Triangulation technique of this research consist of observation, interview and document review. Triangulation technique used to diagnose mathematics learning difficulties that have experienced by students through several stages of existing diagnostics. The data analysis technique used was Miles and Huberman models consisting of: data reduction, exposure data, and drawing the conclusions. The results of this research shows that the kind of difficulty in mathematics study of circumference and wide of two-dimentional figure that have experienced by students were: the students did not understand the concept of the formula with a percentage of 34,6%; errors in the operation of multiplication with a percentage of 16,7%; errors in the operation of division with a percentage of 16,7%; and errors in reading and understanding about the story with a percentage of 34,6%. The factors that cause mathematics learning difficulty were: psychological factors of students who did not like mathematics materials, factors of teacher who have not mastered the materials, and the students lack of family harmony interactions with other family members.Key word: Learning Difficulties, Mathematics Study