Water stress is the most significant abiotic stress factor that restricts agricultural cultivation, causes yield and quality losses, and negatively affects food supply security worldwide. Therefore, it is crucial to explore the effects of water stress on plants. In the present study, we determined the effects of varying concentrations of exogenous nitric oxide (NO) on the morphology, physiology, and biochemistry of cauliflower under different water stress conditions. Four irrigation levels (full irrigation at 100 % as a control – I100 % and water stresses at 20, 40, and 60 %, corresponding to I80 %, I60 %, and I40 %, respectively) and four concentrations of nitric oxide - NO (0, 50, 100, and 150 μM NO, namely, NO0 – control, NO50, NO100, and NO150) were evaluated. The applied water stress negatively affected different plant growth parameters, actual photosynthetic efficiency (PSII), and stomatal conductance (gs) and increased leaf temperature and hydrogen peroxide (H2O2), malondialdehyde (MDA), and proline contents. NO application not only contributed positively to plant growth parameters under stress conditions but also improved PSII and gs. In addition, NO reduced the negative effects of water stress by inducing the antioxidant defense system. The 150 µM NO application contributed to plant growth under full irrigation and water stress conditions.