This study aimed to examine the planning thought and practice that went into the designing of private gardens by Yasuhei Nagaoka. Based on Nagaoka’s statement, in this study, his works were verified using the design documents. A precedent study focused on his planning thought for parks among his works, but the private gardens required unlike these thought. In other words, since private gardens are planned based on architectures that is clearly used to live in, he paid attention to creating harmony between the gardens and the architectures. This is seen from the layouts described in most of architecture places in the gardens planned by him. In particular, most of Nagaoka’s designs were realized in the garden he planned for the residence of Marquis Ikeda in Harajuku. He tried using his planning thought on many private gardens, but these could not be carried out completely. Consequently, it was possible to conclude that the garden of Marquis Ikeda's residence is a typical example of a private garden among his works.