This community service activity aims to foster, assist, and prepare students of SMA Negeri 3 Taruna Angkasa Madiun in facing the National Science Competition (KSN) in the field of Mathematics at the city level. The method used in this mentoring activity is the practice and discussion of high school math competition questions with the online system. Coaching is done using a zoom platform that has been prepared by the coach for 90 minutes for one time coaching. The benefit of this mentoring is that students are able to understand how to solve various models of competition problems. The result of KSN preparation assistance activities in mathematics is the improvement of the ability to solve KSN problems, especially the field of combinatorics, number theory, geometry, and algebra. This can be seen from the results of problem solving by students who were accepted during coaching. In addition, the results of the training are also seen from the results of the city-level selection test in 2021, out of 5 students sent there are 3 students participating in the competition online with good results even though the results are still in the waiting process.