Aim: The aim of this in vitro study was the evaluation and comparison of shear bond strength and microleakage of two nano restorative materials; nano composite and nano resin-modified glass ionomer, commonly used in the restoration of primary teeth. Materials and methods: One hundred and twenty primary teeth were selected for this study. Teeth were divided into two main groups for testing shear bond strength and microleakage. In each of the two groups, teeth were further subdivided according to the restorative material used; nano composite and nano resin-modified glass ionomer. Push out shear test was done using a universal testing machine. Debonded areas were examined and the mode of failure was recorded. For microleakage assessment, Class V cavities were prepared on the buccal surface of each primary molar. Samples were then immersed in methylene blue dye and sectioned longitudinally to examine the tooth restoration interface. Results: There was a significant difference between the two restorative materials regarding shear bond strength while there was no significant difference between them regarding microleakage. Conclusions: Shear bond strength values of nano composite were significantly higher than nano resin modified glass ionomer. There was a statistically significant difference between modes of failure in the two groups. Nano composite showed lower microleakage values than nano resin modified glass ionomer; however, there was no statistically significant difference between them.