The effects of salinity on some growth parameters, protein content and antioxidant enzymes were studied in three Acanthophyllum species of different ploidy levels including A. laxiusculum Shiman-Czeika (diploid species with 2n = 30), A. sordidum Bunge ex Boiss. (tetraploid species with 2n = 60) and A. glandulosum Bunge ex Boiss. (hexaploid species with 2n = 90). Seedlings of the species were subjected to NaCl stress (50, 100, 150 and 200 mM) for 40 days. Salinity affected the growth parameters and caused a reduction in germination percentage, relative growth rate (RGR) and relative water content (RWC) with a greater reduction in A. laxiusculum. However, salinity stress caused only slight decrease in RGR and RWC of A. glandulosum and A. sordidum. Protein content in both A. laxiusculum and A. sordidum increased up to 150 mM NaCl, but this increase in A. glandulosum occurred at 150 and 200 mM NaCl. A. laxiusculum exhibited a decrease in peroxidase (POX) and polyphenol oxidase (PPO) under NaCl stress; while A. glandulosum showed a remarkable increase in POX and PPO between 50 to 200 mM NaCl. In A. sordidum, POX and PPO activities increased at 50 mM NaCl and then decreased at higher salinities. The obtained results showed that the differences in the antioxidant enzyme activities of seedling may, at least in part explain the greater tolerance of A. glandulosum comparing to A. sordidum and A. laxiusculum. According to our results, A. glandulosum (hexaploid species) showed a better protection mechanism against salinity induced oxidative damage than A. sordidum (tetraploid species).