[en] Phragmites karka (Retz.) Trin. ex Steud. is a halophytic grass found in inland saline marshes potentially useful for biofuel industry. Growth, polyphenol content and antioxidant activity in different plant parts were investigated after 45 days NaCl (0,100, 200 and 400 mM) treatments. An increased in polyphenolic content (5.06 to 12.81 mg GAE g-1 DW) and antioxidant activity (0.64-3.21 IC50 mg ml-1 for DPPH and 9.09-17.91 mM Fe+2 g-1 DW for FRAP) was observed with the increasing salt concentrations among different plant parts. Increase in plant biomass, phenolic content and antioxidant activity with lower MDA at 100 mM NaCl indicates a strong protection against oxidative damage. Leaves exhibited highest polyphenol and antioxidant activity, followed by stem and root. Coefficient of regression shows the high predictability of antioxidant activity (0.705) and phenolic contents (0.763) with an increase in salinity. Our data indicates a link between production of polyphenolic antioxidants and salt stress in P. karka which indicates salinity as an effective tool to produce antioxidant rich biomass for industrial purposes. (author)