In order to evaluate the crystallization tendency of glasses, the ratio of the crystallization temperature to the liquidus temperature (Tc/TL) was obtained by DTA measurement for the Na2O–B2O3and Na2O–B2O3–Al2O3systems. The critical cooling rate for glass formation (Q*) was also measured. The measurements were performed in the composition range of (100 −x)Na2O–(x)B2O3, (x= 25–35 and 60–100 mol%), and (100 −y)0.5Na2O·0.5B2O3−(y)Al2O3, (y= 6–34 mol%). The relationship betweenTc/TLandQ* was discussed. A linear relationship betweenTc/TLand logQ* for these systems was found. Furthermore, the relationship betweenTc/TLandQ* was verified by computer simulation based on the crystallization kinetics of glass o