Purpose: To assess the effect of pH cycling on surface microhardness and fluoride release of two modified nanoclay glass ionomer restorations (in vitro). Materials and Methods: A total of 180 permanent human caries free premolars were used. Class V were prepared on facial surfaces of the teeth. They were classified according to type of glass ionomer used for restoration of the cavities into three groups (60 teeth each); conventional glass ionomer medifill (A1), Dellite 43 modified glass ionomer (A2), and Dellite LVF modified glass ionomer (A3). Each group was moreover subdivided into three subgroups (20 teeth each) relative to the immersion solution used. The First subgroup remained in distilled Water (B1 control), the second subgroup was stored in artificial Saliva (B2) whereas the third subgroup was subjected to PH cycling (B3). Microhardness and fluoride release were measured after 7 and 30 days respectively. Results: There was a significant difference in the mean microhardness and fluoride release between the different materials after pH cycling (p≤0.001). PH cycling reduced the mean microhardness of the materials but induced the highest fluoride release. Conclusion: The proposed pH cycling model affected the microhardness of the tested materials while improved their fluoride release. Although the incorporation of montmorillonite into glass ionomer liquid improved the microhardness of the materials but it had yet, no effect on its fluoride release.