Objectives: The purpose of this study was to evaluate the shear bond strength of three bonding systems for two different machinable glass ceramic materials. Methods: Different-shaped specimens were fabricated from two types of machinable glass ceramic block {Cerec 2 Vitablocs Mark II (Vita) and GN-I ceramic block (GC)} using a low-speed cutting saw. Ceramic specimens surface was ground with silicon-carbide paper (#1,200) and etched with a phosphoric acid gel. Different-shaped specimens were then bonded together with one of three bonding systems {GC Ceramic Primer (GC) + Linkmax HV (GC) (CP+LM), Mega Bond (Kuraray) + Panavia Fluoro Cement (Kuraray) (MB+PFC), and Clapearl Bonding Agent (Kuraray) + Clapearl DC (Kuraray) (CBA+CL)}. Specimens were stored in water at 37ºC for 24 hrs and thermocycled 20,000 times before shear bond strength testing. Means and SDs (in parenthesis) of shear bond strength (MPa) are listed. Data were analyzed by ANOVA and Tukey-Kramer test. Results: Cerec; CP+LM:41.5 (6.1)^a, MB+PFC:39.1 (5.7)^a, CBA+CL:46.9 (7.3)^a, GN-I; CP+LM:31.4 (3.6)^a, MB+PFC:10.1 (8.8)^b, CBA+CL:3.0 (1.1)^b. Different superscript letters denote that bonding systems are significant different at each ceramics (p<0.05). The shear bond strength of each bonding system for the Cerec ceramics was significantly higher compared with the GN-I ceramics. For the Cerec ceramics, no significant differences in bond strength were observed between three bonding systems. On the other hand, for the GN-I ceramics, the CP+LM group showed the greatest bond strength among three bonding systems. Conclusion: These results suggest that an effective bonding system should be selected for each machinable glass ceramic material.