Environmental stresses such as drought and salinity limit the availability of water and nutrients to plants; thereby, reducing the quality and quantity of crops yield. Considering the roles of potassium and zinc in plant performance, this investigation was carried out to evaluate the effects of these two elements on growth and some physiological parameters of tomato under water and salinity stresses in a solution culture system. The experiment was conducted in a greenhouse in Soilless Culture Research Center, Isfahan University of Technology, in a factorial arrangement based on a completely randomized design with three replications for water and four replications for salt stress. The water stress was induced using polyethylene glycol 6000 at different levels of 0, 55 and 110 gr l -1 and for salt stre NaCl was applied at 0, 40 and 80 mM. Three levels of potassium (0.6, 3 and 6 mM) a KNO 3 and three levels of zinc (0, 1 and 2 µM) as ZnSO 4 were also included as the K and Zn treatments, respectively in the experiment. The results showed that the water stress led to a significant reduction in the plant height, shoot and root dry weights, relative water content (RWC), leaf water potential, sulfhydryl groups and a significant increase in chlorophyll content, root ion leakage and proline content. In contrast, the 40 mM NaCl treatment caused a significant increase in plant height, shoot and root dry weight, RWC and a significant reduction in proline, but a significant increase in chlorophyll content and root ion leakage and a significant decrease in leaf water potential with the increasing salt stress. Water stress increased the shoot potassium and zinc contents, while the salt stress markedly increased the shoot Na content and decreased K as well as K/Na ratio. The potassium and zinc treatments seemingly alleviated the adverse effects of water and salt stresses with the exception of root ion leakage which increased by potassium application in both stress conditions. The increases in root dry weight, excised leaf water retention (ELWR) and leaf water potential under both stress conditions and sulfhydryl groups, RWC and shoot dry weight in water stress were greater when potassium and zinc applied together as compared with the individual potassium and zinc applications. The interactions of water stress × potassium × zinc, significantly affected the height, shoot and root dry weights, K concentration, ELWR, proline, chlorophyll content, root ion leakage, while the interactions of salt stress × potassium × zinc showed a significant effect on height, Zn concentration, K/Na, ELWR, leaf water potential and chlorophyll content.