Professionalization of Korean interior design is not completed, considering the fact that accreditation and registration systems cannot be found in it. This study, initiated with this concern, analyzed the knowledge area of interior design and architecture in the United States while utilizing accreditation standards of CIDA and NAAB. The purpose of this study is to provide reference to consult for the professionalization of Korean interior design by showing the effects of standardized professional knowledge on professionalization. The utilized research method is a multiple case study, analyzing cases of interior design and architecture in the United States. The unit of analysis is accrediting criteria, including present and revised versions. Content analysis was conducted to interpretate qualitative data collected. The research results include that knowledge differences between interior design and architecture are not clear. This study concludes that standardized professional knowledge emphasizes the technicality elements of knowledge to protect the health, safety and welfare of the public instead of indeterminacy elements. The research results imply that knowledge standardization concerning HSW can be a critical step to professionalization because it can show a jurisdictional boundary as a unique profession.