This research aimed to study the effect of Course Review Horay towars the student's mathematical concept understanding skill. This was an experiment research with Posttest Only Control Design and the populations were all seventh graders of SMP Muhammadiyah 1 Purwokerto. The samples were taken using Cluster random sampling containing of two classes which were class VII A as the experiment class using Course Review Horay and class VII E as the control class using direct learning. The data analysis of this research was independent sample T-test. The results showed that the student's mathematical concept understanding skill with Course Review Horay was better than those with direct learning. In other words, there was an effect of Course Review Horay towards the student's mathematical concept understanding skill in SMP Muhammadiyah 1 Purwokerto.