The purpose of this study was to analyze the features of the avant-garde architecture in the end of the 20th Century based on the ontology as a metalanguage. In view of the results so for achieved, it is possible to say that the thought of becoming, topology, rhizome thought and the Deleuze's concepts of the fold and the event as ever-changing and evolving at any given time are found in the avant-garde architecture, and the introduction of ontological thought into architectural design encourage hopes for a more natural and existential quality in architecture. However, the avant-garde architecture in the end of the 20th century disclosed the limitation in the architectural expression of ontological thought due to the lack of fully understand on ontology. In conclusion, the ontological approach in architecture offers a new morphological methodology and a new way of programming considering the existential aspect of space through the bricoleur's means leaving the ontological meaning of architecture itself.