Understanding the concept of Arabic syntax is a learning problem faced by the students. For that reason, this study aims to improve students' understanding of Arabic syntax. This study employed action research design by presenting six critical-reflective steps in efforts to improve students' understanding of Arabic syntax at a junior high school in West Java, Indonesia. Data were collected using interviews, observations, surveys, oral and written tests. The findings revealed that the understanding of Arabic syntax for first-year high school students regarding noun, verb, particle and sentence material improved well. This study confirms that through a series of critical-reflective steps, the students' understanding of the concept of Arabic syntax can be improved.