The aims of this study are; (1) to investigate Al-Islam learning achievement among students of SMA Muhammadiyah Pleret Bantul; (2) to investigate interpersonal akhlak of the students of SMA Muhammadiyah Pleret Bantul; (3) and to investigate the impact of students’ understanding of PAI on the interpersonal akhlak of students in SMA Muhammadiyah Pleret Bantul. This study is a quantitative research with descriptive approach. The sampling technique employed in this study is simple random sampling with sample consisting of 54 students. Data is gathered through questionnaire and documentation. The collected data is then analysed using descriptive analysis and the hypothesis is tested using simple linear regression test. The result of this study reveals that; 1) the students of SMA Muhammadiyah Pleret Bantul shows great learning achievement in Al-Islam, with 78% of them have great learning achievement; 2) The interpersonal akhlak of the students of SMP Muhammadiyah Pleret is average where 55% of the total respondent is considered to be average; (3) the value of R- square of the summary model table is 0,016 indicating that the effect of akhlak learning achievement on the student’s interpersonal akhlak is only 1,6%. Thus, it can be concluded that al-Islamlearning achievement does not have significance on the interpersonal akhlak of the students in SMA Muhammadiyah Pleret. There are 98,4% other factors that have impact on the interpersonal akhlakof the students of SMA Muhammadiyah Pleret.