Mario Botta is one of the modern architects who established his own architectural world on the basis of the architectural spirit of Modernism. His works have been a good theme not only for those who study architecture but also for those who study the relationship between architecture and the surrounding environment and there have been many published papers and reports on his works. However, most of them stressed on the importance of the external appearance of architecture or on the relationship between architecture and the surrounding environment. There have been relatively few studies that have dealt intensively with interior space. The aim of this study is to find the characteristics of interior space in public buildings that were designed by Botta and to analyze them from the view design principles and design elements. For this purpose, the five most important public buildings were selected and the public space of the building like the central hall, the lobby, and the foyer were analyzed. Through this study, the followings are realized. A) Spatial features: $circled1$ Refined and graceful interiors where the principle of symmetry was applied, $circled2$ Centripetal interiors surrounded by thick walls, $circled3$ Interior design lit by skylights above the central area, B) Formative features: $circled1$ The shapes of the external and internal spaces are identical, $circled2$ Simple geometrical shapes were applied in defining the shapes of internal spaces, $circled3$ Skylights and light wells were combined and were utilized as form elements, $circled4$ Architectural vocabularies of Corbusier such as stairs, round pillars, and bridges were developed and utilized, $circled5$ Utilized the geometry that resembled his architecture as a form element to the furniture, C) material pattern features: $circled1$ Plainly expressed the patterns of bricks that appear in the course of construction, $circled2$ Made and used horizontal stripe patterns using stones of different colors.