133 _______________________________________________________ DOI: https://doi.org/10.33258/birle.v3i1.765 Development of Students Work Sheet Based on Realistic Mathematic Approach with Ethnomatematic nuanced to Improve Critical Thinking of 4 th Grade Students in Primary School (SD Negeri 091358 Haranggaol, Haranggaol Horisan Sub-District) Ester Emerita Tarigan 1 , Hasratuddin 2 , Kms. M. Amin Fauzi 3 1 Master Student in State University of Medan, Indonesia 2,3 Lecturer in State University of Medan, Indonesia Estertarigan69@gmail.com I. Introduction Primary School / Madrasah Ibtidaiyah (SD / MI) is the initial basic education before entering Junior High School / Madrasah Tsanawiyah (SMP / MTs). Education in Elementary Schools or Madrasah Ibtidaiyah is emphasized on the formation of the personality and mentality of students (Prastowo, 2013: 14). Considering the importance of basic education in SD / MI, the government always strives to improve the quality and relevance of basic education through: curriculum development, improvement of teacher professional abilities, development of quality and excellence in basic education, and development of teaching facilities and materials. To follow up on the relevance of education, the government intensively reforms the curriculum and procures relevant textbooks used in schools. This is because books are inseparable in the learning cycle. Without books a learning will be lame. The more supporting books, the more interesting learning will be. This is no different in the case of elementary school children who are still in the concrete development stage, namely having to use interesting and contextual learning media, both in appearance and in content. Abstract This study aims to develop students' worksheets based on a realistic mathematical approach with Ethnomatematic named on rounding numbers in 4 th grade of primary school (SD Negeri 091358 Haranggaol, Haranggaol Horisan Sub-District). The object of this research is the Student Worksheet based on Realistic Mathematics Approach in Ethnomatematic nuance. The instrument used in this study was the mathematics learning achievement test and student response questionnaire. Data were collected and analyzed with quantitative descriptive analysis techniques. This research method is Borg & Gall development research combined with Dick & Carey's learning development model. The test subjects consisted of material and design learning experts, two linguists, using trial I and trial II. The results showed (1) The results of the expert test of subject matter on the assessment of the appropriateness of the content and the feasibility of the presentation were in very good criteria (85.42%); (2) The results of the learning design expert test were in very good criteria (94.23%); (3) Linguists' test results are in very good criteria (94.44%); (4) The results of trial I are in good criteria (60%); (5) The results of trial II are in very good criteria (90%). Keywords Student Worksheet, Realistic Mathematics Approach,