Microstructural control of CaOAl 2 O 3 SiO 2 (CAS) glass-ceramics (GCs) bearing metastable CaAl 2 Si 2 O 8 , a layered crystal, from a parent glass having a single composition was achieved by increasing the amounts of WO 3 and carbon used as sources of metallic W particle nucleation agents. The average crystal size increased from 9.3 to 49 ¯m when the amount of WO 3 and carbon were increased fivefold in the preparation of CAS GCs. To investigate the effect of WO 3 and carbon separately, glass cullet containing WO 3 was mixed with glass batches containing carbon and then melted to form glass specimens with different amounts of WO 3 and carbon. Upon crystallization of these glass specimens, the average crystal size increased from 9.0 ¯m to 43 or 49 ¯m when the amount of WO 3 or carbon was increased fivefold, respectively. The results indicate that changing the amounts of WO 3 and carbon is necessary to control the CAS GC microstructure.