eng Science and Education Publishing American Journal of Educational Research 2327-6150 2018-10-28 6 10 1414 1420 10.12691/education-6-10-12 EDUCATION201861012 article Khairun Nisak Nasution nisak.nst@gmail.com 1 Edi Syahputra 1 Mulyono 1 Post Graduate Program in Mathematics Education, State University of Medan, Medan, Indonesia This intervention study focused on: (1) analyzing whether there is a significant effect of guided inquiry learning model based on Deli Malay culture context towards student's mathematical critical thinking ability or not and (2) analyzing whether there is a significant interaction between learning model and prior mathematical ability towards student's mathematical critical thinking ability or not. This study is a quasi experimental research that used mathematical critical thinking ability test. Population in this study are all students in SMPN 1 Tebing Tinggi Academic Year 2017/2018 and the samples are 32 students in class VIII-A taught by using guided inquiry learning model based on Deli Malay culture context and 32 students in class VIII-C taught by using expository learning. The data was analyzed by using Two Way Anova and found that: (1) there is a significant effect of guided inquiry learning model based on Deli Malay culture context towards student's mathematical critical thinking ability and (2) there is no a significant interaction between learning model and prior mathematical ability towards student's mathematical critical thinking ability. http://pubs.sciepub.com/education/6/10/12/education-6-10-12.pdf mathematical critical thinking ability guided inquiry learning