Abstract This study investigated the effect of thermal stress on the shear bond strength of four commercially available porcelain repair materials. Porcelain cylinders were made and embedded in acrylic resin. Composite resins were bonded to the porcelain samples by using the four organosilane systems. The specimens were aged in 37 °C distilled water for 24 hours. Ten specimens per system were then thermocycled for 48 hours. Ten specimens per system remained in 37 °C distilled water for 48 hours. All samples were loaded at the composite resin/porcelain interface by using an Instron machine. Results demonstrated cohesive porcelain failures for most of the nonthermocycled specimens. Thermocycling caused a significant decrease in the bond strengths of the Command Ultrafine, Enamelite 500, and Fusion materials. Only the Scotchprime system maintained consistently high shear strength values under the conditions tested.