In this study, the responses of onion to drought and salinity stress were investigated. In the research, a total of 15 treatments were designed including water stress levels (I1: non-stress, I2: %25 water stress, I3: %50 water stress) and different NaCl concentrations (S1: 0.3 dS/m-control, S2: 2.5 dS/m, S3: 5.0 dS/m, S4: 7.5 dS/m, S5: 10.0 dS/m). During the experiment, 9.25, 7.66 and 6.07 L/pot irrigation water was applied to I1, I2 and I3 treatments, respectively. As a result of the study, both drought and salinity stress showed destructive effects on the agro-morphological parameters of onion. Especially salinity levels above 7.5 dS/m triggered significant decreases in yield and yield components in onion. Onion yield decreased by 17.3% in S2, 30.3% in S3, 37.5% in S4 and 56.2% in S5 compared to the control group (S1) according to salinity levels. When the effects of water stress and salinity stress were evaluated separately, the highest membrane damage (58.4%) was determined in severe water stress treatment (I3), and the highest H2O2 content was determined in severe salinity stress treatment S5. On the other hand, antioxidant enzymes such as catalase (CAT), peroxidase (POD) and superoxide dismutase undertook more significant tasks under salinity stress compared to water stress and these enzymes reached maximum values especially under severe salinity stress. Increasing salinity stress decreased the water productivity (WP) of onion, whereas increasing water stress provided significant increases in WP values. According to the obtained data; the use of water with electrical conductivity above 2.5 dS/m in irrigation shows that there will be significant yield decreases in onion. On the other hand, it was clearly understood from the results of this study that 25% to 50% water saving can be achieved by deficit irrigation in onion cultivation in water stressed environments.