The aim of this work was to study the effect of metal oxide nanoparticles (MO NPs) on enzymatic activities (EAs) of two main plant life forms under drought stress (DS). Foliar spray of silver oxide (AgO), iron oxide (FeO), zinc oxide (ZnO) and cadmium oxide (CdO) at levels of 30, 60, 90 and 120 mg.L-1 were used on aerial parts of forb Sanguisorba officinalis L. and grass Agropyron cristatum (L.) Gaertn. under DS levels of 25-100% field capacity (FC). Glutathione reductase (GR), catalase (CAT), peroxidase (POD) and superoxide dismutase (SOD) were measured after two weeks of the experiment. The results indicate that the EAs changes varied depending on the plant life form, levels of DS, type and levels of NPs. Overall, application of 30- 60 mg.L-1 MO NPs under 25-50%FC significantly reduced EAs, especially in forb (P<0.001). Higher concentration of MO NPs significantly increase EAs. A decrease in CAT (20.90%, 18.80%), POD (21.30%, 17.67%) and SOD (23.14%, 16.88%) was observed under levels of 60 mg.l-1 of ZnO NPs under 25-50%FC in forb and grass, respectively. High concentration of CdO NPs (90-120 mg.l-1) caused by increase (max= 24.0%) in EAs in both life forms under 25%FC.