Nowdays, aboundant agricultural waste is produced in Iran. Pistachio is one of the most important crops in Iran which is about 52% of pistachio world production in 2013. Pistachio shell is an agro-waste with attractive source of cellulose that can be used to produce tiny and useful cellulose nanocrystals (CNC). Alkali and bleaching treatments were performed on these pistachio shells to remove hemicellulose, lignin and non-cellulose components to purify cellulose. The yield of cellulose extraction was 44%. In order to obtain cellulose nanocrystals, acid hydrolysis with H 2 SO 4 and HCl were performed. Acid hydrolysis with H 2 SO 4 damaged the crystalline regions and created amorphous structure from the beginning of the hydrolysis time. Whiel, HCl was a milder acid, removed amorphous structures and produced CNCs. Hydrolysis was performed under different times (120, 180 and 240 min) and HCl concentrations (2 and 3 M) at 100 with acid to cellulose ratio of 40 ml/g under hydrothermal conditions to create cellulose nanocrystals with higher yield and lower size. HCl with 3M concentration and hydrolysis reaction time of 180 min were recognized as the optimum conditions to extract CNCs by the yield of 77.1% and crystallinity 79.4%. Spherical nanoparticles with mean diameter of 69.8 ( 20.7) nm were observed by TEM analysis. Chemical structure and thermal properties of CNC were characterized by FTIR and TGA analysis. According to FTIR analysis, hemicellulose and lignin were removed while the crystallinity index of CNCs were enhanced. Also TGA analysis represented the decreases in thermal stability of CNCs. Also the CNCs were used to stabilize 10% oil in water emulsion. By increasing the CNC concentration, the stability of emulsions to heating, stresses and long storage enhanced while the mean diameter of oil droplets decreased. On the other hand, the CNCs were used as a carrier to encapsulate peppermint oil. By increasing the peppermint oil concentration (10 to 50%), encapsulation efficiency increased from 18 to 44%. The controlled release of CNC-PO in simulated saliva was evaluated. Chemical structure and crystallinity degree of CNCs after encapsulation were characterized. The FTIR analysis showed the main peaks of peppermint oil in CNC-PO spectra while the crystallinity index were decreased slightly after encapsulation. The results of this study indicated that because of low environmental impact of cellulose, using these CNCs for emulsion preparation and bioactive encapsulation is preferable. Keywords: Cellulose nanocrystal, Emulsion, Encapsulation, Peppermint oil.