Proportional reasoning as a qualitative structure that allows complex physical systems comprehension which contain many factors. On physics learning, student’s proportional reasoning ability is expected to be trained and developed because physics learning has part related to reasoning. The purposes of this research are: (1) gaining information of student’s proportional reasoning ability in physics learning; (2) gaining information of student’s obstacles in developing the proportional reasoning ability. The used research’s method is ex-post facto with research subject is students in XI IPA 1 SMA Negeri 1 Gelesong. This research uses statistical descriptive analysis to describe student’s proportional reasoning. From the research result, it can be said that (1) the proportional reasoning ability of students is still low in physics learning. (2) there are some obstacles in developing the proportional reasoning in physics learning which are the less effort given by their teacher to use the proportional reasoning as a device to solve physics problem, students do not use proportional reasoning method because they are not sure whether their answer will be accepted by the teacher.

Keywords : Proportional reasoning, physics learning.