Abstract-This research is a quantitative research, which aims to find a valid and reliable instrument for testing the mathematical reasoning ability for junior high school students. The process of analysis this instrument starting from (1) a literature review, (2) the preparation of the instrument, (3) the teoritical validity, that is testing the readability limited to five students and test the validity by experts, (4) revision, (5) the empirical validity, and (6 ) data analysis. Readability test is applied to five students with the choosen materials. Expert's judgement conducted by two supervisors, three lecturers of mathematics eduction, a junior high school math teacher, and a bahasa lecturer. Empirical validity was done in 9th grade in one of junior high schools in Bandung. The results obtained in the form of mathematical reasoning ability test instruments are valid, each coefficient validity item is more than 0.41 that mean degree of validity was high and very high. The coefficient reliability was 0.64 (more than 0.41) belonging to the high level of reliability. Thus, mathematical reasoning ability test can be said as valid and reliable so that it was classified as good instrument.