Composite YAG/Nd:LuAG transparent ceramics were fabricated by a thermal bonding process. The spatial distribution of ions around the original bonding interface of the YAG/Nd:LuAG composite laser ceramic was investigated. Around the original bonding interface, Lu3+ and Y3+ ions were replaced with each other in dodecahedral symmetry sites. Results from X-ray photoelectron spectroscopy (XPS) and energy dispersive spectroscopy (EDS) quantitative chemical analyses positively show that the distance of Y3+ ions diffused in the LuAG part is about 35 mu m, while Lu3+ ions' diffused distance in the YAG part is about 5 mu m. This corresponds to the diffusion coefficient of Y3+ ions and Lu3+ ions (D-Y=2.43 x10(-10) cm(2)/s and D-Lu=0.56x10(-10) cm(2)/s at 1750 degrees C). The formation of YxLu(3-x) Al5O12 polycrystal in the bonding section explains the complete combination of LuAG and YAG without a bonding interface. Moreover, no diffusion phenomenon of Nd3+ ions was detected near the original bonding interface.