To evaluate the effect of chitosan NPs on wheat under late season drought stress, a factorial experiment was performed based on a randomized complete block design in three replications in pot conditions at Tarbiat Modares University in 2015. The experimental factors included the NPs concentrations (0, 30, 60 and 90 mg.L^-1), application methods (foliar and soil application) and irrigation regimes (normal irrigation and removal of irrigation 15 days after pollination). Experimental procedure includes planting seeds and then prepared chitosan NPs suspension added to them through soil and foliar application in three stages (tillering, stem elongation and heading). Results indicated that the drought stress significantly decreased amount of carotenoid, chlorophyll a, b, total, photosynthesis, stomatal conductance, transpiration, yield, 1000- grain weight as well as biomass and increased intercellular CO₂ concentration (Ci). In most studied traits, no significant difference was observed between consumption methods of nanoparticles. In both irrigation regimes, applying NPs especially concentration of 60 and 90 mg.L^-1 significantly improved the majority of studied traits. In general, application of chitosan NPs reduced negative effects of drought stress in wheat plants and improved growth.