Glass ceramics consisting of fluor-phlogopite can be machined with tight tolerance with conventional metal working equipments and tools. These ceramics are used for a few mechanical and electronic parts. The purpose of this paper is to study bonding material of diffusion bonding and to find the mechanism of bonding with high efficiency. The tests of diffusion bonding were conducted on a electric furnace and heating temperature was varied from 1100 K to 1300 K. The main results obtained are as follow: (1) The bonding strength of machinable ceramics has a great influence heating temperature and time. (2) The high pressure of boundary surface in the diffusion bounding was increase bonding strength. But, bonding strength was held constant at pressure above 0.08 Mpa. (3) The bonding material of boric acid-solution was possible to obtain a high bonding strength at short time.