This research was conducted at the faculty of agriculture, Ain Shams university, Shubra El-kheima. The research aimed to test the effect of selenium (Se) and nano-selenium (NSe) on green bean to mitigate the cold temperature stress. Green bean seeds were sown late (mid-December) with low temperatures in open field (open) and under low tunnel (cover). Green bean plants were sprayed with selenium (Se) or nano-selenium (NSe) with four concentrations (0, 2, 4and 8 ppm). Cultivating green bean under low tunnel produced the highest vegetative and yield characteristics compared to open cultivation. Spraying plants with 8ppm NSe significantly increased the following parameters in the first season (2017) and second season (2018), respectively: plant height was (48.50 and 45.83 cm), number of leaves (7.17 and10), and nitrogen % in leaves (4.13 and 5.28), yield (2872 and 3029 gm) and reduced proline content in leaves (825 and754) compared to 0 ppm. Spraying green bean plants with NSe enhanced the following parameters; plant height (48.50 and 45.83 cm), number of leaves (48.50 and45.83), nitrogen % in leaves (6.13 ,and5.78 ),and yield (2479 and2749 gm).while, reduced proline content in leaves (1148 and 1122) compared to Se. Regarding concentration effect data showed that 8 ppm resulted the highest total yield (2747 and2949 gm), number of leaves ( 14.08 and 14.08), plant height( 47.33 and 45.29 cm) while reduced proline content in leaves (922 and834.5) compared to other concentrations. Lastly, 8 ppm NSe under cover obtained the highest total yield (3045 and 3178) compared to other treatments.