Soil and water salinity is a major constraint in arid and semi-arid regions, lowering plant growth and productivity due to negative effects on plant physiological processes. Areas with saline and sodic soils are expanding in Iran, nearly 12.5% of agricultural soils of the country already are suffering from salinity. In order to study the impact of water salinity on physiological characteristics and dry matter production of some flax genotypes, a 4-replicate factorial randomized complete block pot experiment was conducted in Research Green House, College of Agricultur, Isfahan University of Technology, Isfahan, Iran on 2012. Salinity consisted of four levels: 0 (control), 35 (low salinity), 70 (intermediate salinity) and 105 (severe salinity) mM of NaCl and genotypes consisted of C 1 , C 2 , C 3 , B, 33 and Khorasan. Leaf chlorophyll (chl) and carotenoid content, proline and soluble carbohydrate content of plant leaf and root and activity of Catalas (CAT), Ascorbate Peroxidase (APX) and Glutation Peroxidas (GPX) in plant areal parts at flowering stage along with plant dry matter (DM) production were measured. Mean plant height at flowering decreased with increase in salinity, though the decrease was genotype–dependent, B indicating the smallest decrease among genotypes studiedin this experiment. Genotypes C 2 and C 3 indicated greatest decreased in plant height among genotypes studiedin this experiment. Severe water salinity led to 36.71, 33.30, 36.28, 2.89, and 60.69% decreases in chl a, chl b, chl total, chl a/chl b and carotenoid, respectively. Mean proline content of plant leaf and root increased by 6.35- and 1.54-fold under 105 mM, compared to the control, respectively. Genotypes C 3 and 33 indicated the greatest (6.4-fold) and smallest (2.8-fold) increases in leaf prolin content, respectively. Khorasan and 33 indicated the greatest increases (3.81 -and 3.8-fold, respectively) and B the smallest (1.22-fold) incease in leaf soluble carbohydrate content. While mean antioxidant activities increased with salinity, the greatest mean enzymes activities were detected with the intermediate salinity level, compared to the low and severe levels of NaCl salt. In contrast to the rest of genotypes, genotype Khorasan and 33 indicated increases in their CAT, APX and GPX activities with severe salinity, compared to the intermediate salinity. Mean plant DM at flowering decreased with increase in salinity, though the decrease was genotype–dependent, Khorasan indicating the smallest decrease among genotypes studiedin this experiment. It could be concluded that flax suffers from NaCl even with intermediate water salinity, due to its negative effects on physiological attributs. Flax genotypes differ in terms of their DM production under salinity. Since Khorasan and 33 indicated the smallest decreases in DM under severe salinity, therefor, they seem to be more resistant to the NaCl salinity at least at their vegetative growth stage. The resistance of the latter genotypes could be attributed, at least in part, to their ability to increase or to keep constant the activity ofCAT, APX and GPX under severe saline conditions. Key Word : Flax, NaCl, Soluble Carbohydrate, Antioxidant, Dry Matter