The aim of this study was to evaluate and compare the marginal fit and microleakage of provisional crown fabricated from polymethyl methacrylate (PMMA) and Nanodiamond modified Polymethyl methacrylate (PMMA) on two different die systems. 44 molars received, and provisional crowns were fabricated according to: Group A: Fabrication on die stone using PMMA. Group B: Fabrication on die stone using PMMA reinforced with Nanodiamond Nanoparticles. Group C: Fabrication on the flexible die using PMMA. Group D: Fabrication on the flexible die using PMMA reinforced with Nanodiamond Nanoparticles. Then marginal discrepancy evaluated with silicone impression replica technique. After the cementation and thermo cycling crowns were stained in 2% methylene blue. Followed by sectioning on buccolingualy and evaluated under a stereomicroscope to obtain digital images. Images were then analysed in software to obtain values for microleakage. Then One-way ANOVA and post-hoc Tukey test was performed. For Marginal accuracy according to ANOVA, the difference is statistically significant with a p-value of 0.015. According to Post-hoc Tukey test the difference between GROUP A and D is statistically significant with a mean difference of 7.95. For Microleakage, according to ANOVA, the difference is statistically significant with a p-value of <0.001. According to the Post-hoc Tukey test, a statistically significant difference was found between all groups.Within the limitations of the study, it can be concluded that in comparison with crowns fabricated using conventional PMMA resin on stone die, the crowns fabricated using reinforced PMMA resin with flexible dies showed less microleakage and marginal discrepancies. Results are within clinically acceptable values. Provisional crowns made with PMMA reinforced with nanodiamond on a flexible die have reduced microleakage