The impact of periodic drought stress on photosynthesis changes was examined inHaloxylon aphyllum and Haloxylon persicum. Parameters F0, Fv/Fm, the chlorophyll content and chlorophyll a/b ratio were measured. Drought stress factor was consideredas lack of irrigation of potted-seedlings of two Haloxylon species in periods 0, 2, 4, 6... 26 and 28 days, and each drought period were repeated six times. Species factor includedH. aphyllum and H. persicum. Drought stress​​ significantly (p=0.01) reduced chlorophyll content and maximum quantum yield of photosynthesis (Fv/Fm ratio) but increased the Chl a/b ratio. Both the species are susceptible to drought stress. Key words: Haloxylon, photosynthesis, stress, drought, fluorescence