Abstract: Superoxide dismutase activity changes were studied at different periodic tensions using of spectrophotometric measurement of decline in NitroBlue Tetrazolium reduction to Blue Formazan at 560 nm in Haloxylon aphyllum and Haloxylon persicum. The aim of this study was to investigate the changes of superoxide dismutase in applied drought stress in two species of Haloxylon. The results showed that the effect of drought stress on increase in superoxide dismutase activity was significant (p≤0.01) in two haloxylon species. Drought increased enzyme activity at severe tensions. When two haloxylon species were placed under 7 and 14 days no-watering treatments (mild tensions), the enzyme activity was more than its activity in control treatment and less than one in 21 and 28 days no-watering treatments (severe tensions). The enzyme activity in branchlets of Haloxylon aphyllum under 21 and 28 days no-watering treatments was 20.2 and 29.5% more than its activity under control treatment respectively. This activity in Haloxylon persicum was 21.6 and 31.4% more than its activity under control treatment, respectively. With the advent of drought, superoxide dismutase activity increased in two species of haloxylon. The increasing of superoxide dismutase activity in time of dryness advent in Haloxylon aphyllum was more than Haloxylon persicum, which can be raised as an acceptable factor and vindicator in being more resistant of Haloxylon aphyllum to environmental drought.