The aim of this research is to find out the implementation of fun school at SMA Negeri 1 Sleman (a public senior secondary school) in Yogyakarta. The method of this research was descriptive qualitative with case study approach. The technique used in collecting data was by field study, documentation, and interview. The source of the data was the headmaster, teachers, and students. The data validity used triangulation technique, while the data analysis used interactive data through some step, that is, data collection, data reduction, data presentation, and verification or drawing the conclusion. The result shows that SMA Negeri 1 Sleman is one of fun schools in the aspect of headmaster's leadership, educator support and education manpower, school environment, infrastructure, learning activity, excellent service, and class climate. The school management focuses on aspects that lead it to be a favorite, high-rank, and fun school. This research concludes that headmaster's leadership is the main indicator to construct the fun best school.