Started by the desire of St. Theresia’s religion section to make a different St. Theresia Day mass from usual, came an idea from 3 persons who at that time were St. Theresia students which are; Stella Indah Sari, Dewi Atmodjo, and Ricky Tjitradjaja to form a small ensemble which consisted of 6 violins, 1 flute, and 1 clarinet. The ensemble made its debut in October 2, 2003.
As time goes by, the ensemble grew into a symphony orchestra with not less than 50 members. The orchestra was named St. Theresia School Orchestra (abbreviated STSO). STSO becomes a place for St. Theresia students and alumnus to enhance their musical skills and experiences.
STSO members consist of students and alumnus of St. Theresia Junior and Senior High School. STSO's activities include routine practice once per week, public concert which was held annually, workshop for STSO musicians, and various performances besides STSO public concert