Abstract:    Introduction: Protecting the vital pulp in deep carious lesions possess a great challenge for clinicians in minimal invasive dentistry. Aim: To assess the pulp response to two montmorillonite modified adhesive systems (with and without organic modifier) in deep dentine cavities in dog's permanent posterior teeth. Materials and Methods: Six-healthy adult mongrel dogs were undergoing general anesthesia through intravenous injection of sodium pentobarbital; a rubber dam was fixed in place; cavities were prepared in labial surface of each tooth. Cavities were divided into three groups according to the restorative materials used: Group1: Prime&Bond universal^TM adhesive (Control). Group2: Dellite®43B modified Adhesive system (with organic modifier). Group3: Dellite®LVF modified Adhesive system (without organic modifier). BulkFill material with Flowable consistency was used to fill the rest of the cavity over tested materials. Each group was subdivided into 3 equal subgroups at time intervals: after 1 week, 30 and 60 days. The study design was performed to obtain a total of 90 dogs' teeth, the number of samples for each material was n=7, and total number of samples in the six dogs for each material 42 teeth in each group, the best 30 teeth were examined. Differences between timepoints was evaluated by Friedman's test, and overall differences induced by groups, timepoints and interaction were assessed using two-way ANOVA. Results: There was no significant difference in pulp response of the conventional prime and bond adhesive system and Dellite43 modified adhesive. A significant difference between the two mentioned materials and Dellite LVF modified adhesive system. Conclusion: Organic modified montmorillonite adhesive produced favorable pulp response and seemed to be a promising biocompatible material comparable to conventional adhesive.