Major prefabricated houses manufacturers started their business around 1960s and became world class large housing companies. This study clarifies 9 major prefabricated houses manufacturers' developments at early stage by interviews with their in-house engineers and architectural designers as well as analysis of relating documents. Early prefabricated houses were developed by small number of engineers intensively. Various architecture and specialists including foreign architecture, famous architects and academics affected these developments in some aspects. Furthermore, each of early prefabricated houses had many unique characteristics in building systems. Some of them had changed in early stages, while the others still remain nowadays.