We have developed the glass ceramics containing ruby crystals by heat treatment of a Cr3+-doped SiO2-Al2O 3-Y2O3 glass at 1550°C. The shape of precipitated crystals in the glass matrix was rod type whose average width and length were around 10 and 200 μm, respectively. From an X-ray diffraction measurement and an electron probe X-ray microanalysis, it was confirmed that the rod crystals were α-Al2O3. Intense emission bands of Cr3+ at 694 nm, called the R-lines, were observed in the glass ceramics heat treated above 1300°C. In addition, the intense red luminescence was observed only in the α-Al2O3 rod crystals by a photoluminescence mapping image. © 2010 The American Ceramic Society.