The way of manufacturing Pelt, Wet blue, Crust, and finishing leather is proposed in which standard sample of collagen fiber about Pelt, Wet blue, Crust and Finishing leather is established and only Pelt, Wet blue, Crust and Finishing leather corresponding to the established standard sample is dealt with in the succeeding process. With applying this way of treatment to the treatment of chemical, of general enzyme and of Bio-tech, a quality prediction for the final product come to be possible from dat about Pelt, Wet blue, Crust, and Finishing leather according to each process. Especially it turns out that the most influencial process among every detail process is an unhairing, and a physical property is wholly improved when processing agent and auxiliary processing agent are put in the manufacturing process. In case of Crust and Finishing leather, the test of every sort of pysical property can get almost the same result.