During the late 19th and early 20th centuries, there was a significant decline in the use of ornamentation in architecture. Louis Sullivan and Adolf Loos were two architects who had contrasting views on the use of ornaments in the beginning of modern architecture. This research explores how Louis Sullivan's and Adolf Loos' views on ornamentation influenced modern architecture. The findings of this study can be used by architects to understand the trend of ornamentation in architecture and why it has largely disappeared to this day. The main research question is "How did Louis Sullivan’s and Adolf Loos’ views on ornaments in architecture influence modern architecture?". The study conducts qualitative literature research on the theoretical writings of Sullivan and Loos and analyses two modern architectural works that exemplify the influence of their ideas on ornamentation: the Guaranty Building (1896) by Louis Sullivan and the Looshaus (1911) by Adolf Loos. The results show that Sullivan used ornamentation to enhance the expression of the function and purpose of the building, while Loos saw ornamentation as a sign of degeneration in modern architecture and opted for simplicity. The emphasis on functionality by Sullivan and Loos inspired modernist architects to design radically functional buildings, which led to the disappearance of ornamentation in the early 20th century.