This study aims to improve the learning process and develop high-level thinking skills of students through the learning process using the International baccalaureate curriculum in 5 th grade students at Siti Hajar Islamic Elementary School. This research is classroom action research (PTK) and carried out in three cycles, where each cycle consists of planning, action, observation and reflection. The aspects observed in each cycle are the activities of students and teachers, as well as the process of learning mathematics in class. The research subjects were 48 students consisting of 24 male students and 24 female students. The analysis of research on students' high-level thinking skills in mathematics learning using the Solo Taxonomy assessment which consists of 4 levels of high-level thinking, namely: (Unstructured, Multi-structural, Relational, and Extended Abstract). From the results of cycle 1, the percentage of students who reached the extended abstract level was 13.33%, in the second cycle, the level of thinking of students at the extended abstract level was 67.53% and in the third cycle the percentage of students who reached the level of extended abstract thinking was 77.33. Based on the indicators of success in the third cycle, the learning process of using the International baccalaureate curriculum in 5 th grade students at Siti Hajar Islamic Elementary School has proven to improve students' high-level thinking skills in mathematics learning. Keywords: International Baccalaureate Curriculum, HOTS, Solo Taxonomy DOI : 10.7176/JEP/10-33-07 Publication date: November 30 th 2019