Water deficit conditions restrict cotton growth and productivity by disrupting plants biochemical and physiological process. Selenium (Se) improves plant physiological and antioxidant properties under stress conditions. The current study was carried out in 2020 and 2021 seasons at Mallawi station, Cotton Research Institute, Agricultural Research Center, Minya, Egypt. The experiment design was split-plot with three replications, which main plots were devoted to irrigation intervals treatments of normal irrigation (NI) and irrigation water deficit (IWD), while the sub-plots were randomly of spraying Se in mineral and nano-forms (mSe and nSe) at 50 and 100 ppm concentration at twice squaring and flowering stages to evaluate the effect of mSe and nSe on leaves chemical constituent, growth, yield, fiber and yarn properties of Giza 95 cotton cultivar. The results stated that IWD conditions reduced significantly pigments, yield, fiber and yarn properties, whereas increased significantly enzymes activity and osmoprotecant compounds compares to NI conditions. Foliar application of Se enhanced significantly all chemical constituent, growth, yield, fiber and yarn properties, which nSe (50 ppm) recorded the highest results then nSe (100 ppm) and mSe (100 ppm) compared to untreated plants. The interaction between two factors affected significantly in almost studied parameters, which the maximum values gave by spraying nSe (50 ppm) then nSe (100 ppm) comparing with control under NI and IWD conditions in both seasons. Finally, selenium nano particles were more effective in all studied parameters especially under IWD conditions to amelioration the adverse effects of stress conditions.