AbstractWe are developing high average power laser materials based on silica glass. The uniform dispersion of rare earth ions in SiO2 glass, which is the most difficult thing to make laser material, was achieved by using rare earth distributed Zeolite X. Nd doped SiO2 glass shows enough properties as a laser material, but its spectroscopic properties are weaker than commonly used phosphate glass. Some trial for improving the spectroscopic properties are done and it is shown that the co-doping effect in supercage of Zeolite X and that phosphoric acid treatment are useful.