Introduction: This study was carried out to evaluate the microshear bond strength of two types of high viscous glass-ionomer restorative materials (conventional and filler modified) bonded to normal and caries-affected dentin.Materials and Methods: A total of 48 teeth with carious crown segments were selected. Teeth were sectioned 2mm gingival to the CEJ to expose the pulp chamber. Then, a polymethacrylate plate with central hole was glued to crown segment. A 19 gauge stainless steel butterfly needle was checked to be fit to the central hole of the methacrylate plate and to the pulp chamber of the tooth. The crown segment was then embedded to the level of the CEJ in a mold using a chemically cured polyester resin. Then, the occlusal portions of crown segments were ground to expose flat dentin surface. Two different methods (caries-detecting dye and dye permeability test) were used to differentiate caries-affected dentin and normal dentin. The crown segments (n=48) with normal and caries-affected dentin were divided into two groups (n=24) according to the tested type of glass-ionomer used; (Fuji IX; High viscous glass-ionomer) or (ChemFil Rock; Filler modified glass-ionomer). Glass-ionomer micro-cylinders were bonded to the dentin surface. Micro-shear bond strength test was done using a universal testing machine. The obtained data was then recorded, tabulated and statistically analyzed. Failure mode was determined using an Environmental Scanning Electron microscope (ESEM). Frequency of the mode of failure was expressed as percentage value for each group. Representative Scanning Electron microscope photomicrographs of each type of failure were captured at various magnifications. Results: Two-way ANOVA revealed no statistical significant difference between the two glass-ionomer restorations values [(Fuji IX GP; High viscous glass-ionomer) and (ChemFil Rock; Filler modified glass-ionomer)] (P= 0.06), and dentin substrates (normal and caries-affected dentin) (P= 0.32), as well as the interaction between the variables (materials and dentin substrates) was not statistically significant (P= 0.08). There was no statistical significant difference among the mean microshear bond strength values of the Fuji IX GP and ChemFil Rock glass-ionomer restoration bonded to both substrates (P= 0.07). For specimens of the Fuji IX GP glass-ionomer restoration bonded to normal and caries-affected dentin, the fractured specimens were mostly adhesive failure at dentin followed by mixed failure (adhesive at dentin side/cohesive failure in glass-ionomer restoration). While in the ChemFil Rock glass-ionomer restoration bonded to normal and caries-affected dentin, the fractured specimens were mostly mixed failure (adhesive failure at dentin side/cohesive in the adhesive layer/cohesive in cement) Conclusion: Under the conditions of this study, the following conclusions were drawn:1.Filler modified glass-ionomer did not surpass the conventional high viscous glass-ionomer with regarding to the bond strength to both normal and caries-affected dentin.2. Difference in dentin substrates (normal and caries-affected dentin) did not influence the bond strength of any of the tested glass-ionomer cements.