This paper is to reconstruct the design process of Louis I. Kahn's Kimbell Art Museum through a morphological analysis of the basic form and its vocabulary which were applied by the Architect.The sequence of the discussion is as following : 1) An analysis of design sketches etc. to induce the basic form and its vocabulary. 2) An examination of their adaptability to the Museum's architectural program. 3) An explanation of the vault, the main vocabulary in the design, which plays an important role incontrolling the relationship between program requirements and formal transformations in the design.