Shade may cause reduction in quality and yield of crops, however, species and cultivars within species may respond differently to shade. Therefore, the purpose of this experiment was to determine the effect of shade levels on morphological and physiological properties of flax genotypes. The experiment was a split plot based on complete randomized block design with four replications. Seeds were planted in pots and put outside under natural conditions at the Isfahan University of Technology, Isfahan, Iran in 2012. Treatments were five levels of shade ( 0.0, 20-30%, 40-50%, 60-70% and 80-90%) and ten flax genotypes ( SH 10 , KH 25 , CH 14 , KH 22 , KO 11 , KH 40 , KH 13 , CH 10 , KO 12 and KH 19 ). Shading was carried out after 40 days of planting using polyethylene gauzes. Days to 50% emergence, 50% flowering and maturity, plant height, leaf area index, number of capsules per plant, number of seeds per capsule, number of branches per plant, seed yield, seed weight, biological yield, harvest index, seed protein, oil, chlorophyll contents, carotenoid content and leaf proline content were measured during the experiment. The results showed that on average the effect of shading levels on measured traits were significant except that of day to 50% emergence. Shading up to 40-50% increased chlorophyll a, chlorophyll b, total chlorophyll, carotenoid contents and number of seeds per capsule, but these parameters were reduced thereafter. Leaf proline content was decreased up to 40-50% shading but increased thereafter. Day to 50% flowering, day to maturity, plant height, leaf area index, number of branches per plant and seed oil content were increased with increasing shade level. Shading up to 60-70% increased biological yield, but reduced it thereafter. Shading up to 20-30% increased number of capsules per plant, seed yield, seed weight and harvest index. While these factors were decreased beyond this range. Protein content was decreased as shade level increased. The highest (2.58 g/mg leaf) and the lowest (2.08 g/mg leaf) chlorophyll a/b ratio were obtained under 80-90% and 20-30% shading, respectively. There was interaction between shade level and genotype on days to 50% flowering and maturity, leaf area index, number of capsules per plant, number of seeds per capsule, number of branches per plant, seed yield, seed weight, biological yield, harvest index, seed protein, oil, chlorophyll contents, carotenoid content and leaf proline content were significant. The highest chlorophyll a, chlorophyll b and total chlorophyll were obtained in SH 10 under 40-50% shading. The highest carotenoid contents was obtained in KO 11 under 40-50% shading. The highest days to 50% flowering and maturity were obtained in CH 10 under 80-90% shading. The highest leaf area index and oil were obtained in SH 10 under 80-90% shading. The highest number of branches per plant was obtained in KH 40 under 80-90% shading. The number of capsules per plant and seed yield were obtained in KH 22 under 20-30% shading. The highest seed protein was obtained in KH 22 under control (0.0). The number of seeds per capsule was obtained in CH 10 under 40-50% shading. The highest seed weight was obtained in CH 14 under control (0.0). The results showed that shading up to 20-30% increased number of capsules per plant, seed weight, seed yield and harvest index and shading up to 80-90% increased seed oil content. KH 22 and KH 19 were the most and the least shade tolerance genotypes, respectively. Keywords : Flax, Proline, Harvest Index, Shade, Carotenoid