Several studies have related the application of micronutrients such as zinc, iron and molybdenum with alleviation of stress symptoms in horticultural plants. However, there are few studies that correlate the microelements with water relations. The main objective of this study was to determine the effect of the foliar application of Zn on pak choi (Brassica campestris, L.) plants grown under saline conditions. When plants were grown in a nutrient solution containing 0 or 80 mM NaCl, shoot biomass was greatly decreased, while, in a separate experiment, Zn toxicity was observed when it was applied at concentrations above 50 µM as a foliar spray. In a third experiment, low Zn applications, mainly 25 µM, enhanced parameters such as gas exchange, biomass and glucosinolates synthesis in plants grown under saline conditions (80 mM NaCl). Also, Zn application provoked a rise in membrane integrity and decreased oxidative damage in root cells. In conclusion, Zn application decreased oxidative damage and increased the content of glucosinolates, which could act as important signals to improve water uptake and transport and, as a consequence, alleviate salinity stress in pak choi plants.