This paper presents a study on the Palazzo Firenze of B. Ammannati, designed between 1550~1572. He was active in Rome and Firenze in the middle of 16th Century. His most important project, such as Palazzo Pitti, is located in Firenze. But there are some projects that are important as well as Palazzo Pitti in Rome, such as villa Giulia and Palazzo Firenze. Usually, in the history of Western Architecture, the period in which Ammannati was active is denominated as late-Renaissance or Mannerism. In this period there was very important progress in field of artistic theory. There were active many great Masters such as Michelangelo, Vignola and Giulio Romano. But, over the all, the most important characteristic of this period was a transition period between Renaissance and Baroque. This paper try to reveal such characteristics reflected in architectural projects designed in this period, focusing on, over the all, B. Ammannati and his Palazzo Firenze project..