This study aims to (1) develop an integrative thematic textbook for the 1 st grade of elementary school oriented to improve critical thinking skills; (2) to know the feasibility level of integrative thematic textbooks (3) to know the level of legibility of integrative thematic textbooks; and (4) to know the level of effectiveness of integrative thematic textbooks in improving students' critical thinking skills of primary schools. This research method used R & D which refers to 4-D model by Thiagarajan. The test substance was the 1 st grade primary school student. Data collection used observation method, expert validation, readability test, and critical thinking ability test. Data analysis technique used descriptive and t test. The result of the research indicated that the integrative thematic textbook developed has good feasibility in good criteria, practical readability level and can be applied and easily understood, the effectiveness of the module was tested using t test at 0.05 significance level which result 0.000 <α = 0.05 where the critical thinking ability of students which uses an integrative thematic textbook was better than the critical thinking ability of students which only used ordinary textbooks. This textbook can be used to develop the critical thinking skills of elementary school students, especially in low classes.