Jamasan Meriam Nyai Setomi is a traditional ritual at the Keraton Kasunanan Surakarta Hadiningrat to cleanse the sacred heirloom Meriam Nyai Setomi, a relic from the Mataram Kingdom that once served as a weapon for Sultan Agung Hanyokrokusumo. This tradition has been practiced since the reign of Pakubuwono III (1745) and is typically conducted two days before Grebeg Syawal at Siti Hinggil within the palace. The ritual can only be performed with the dhawuh (command) of the Sinuhun (king) and involves specific offerings such as Minyak Boreh, Minyak Koyoh, and Pepak Ageng. Initially, the ritual was exclusively carried out by sworn Abdi Dalem (royal servants), but during the reign of Pakubuwono XII, it was opened to public viewing, although the ceremony is still conducted by selected individuals. Lasting approximately 2.5 hours, the ritual requires participants to wear traditional Javanese attire, remain silent, and recite dhikr and shalawat in their hearts.