Utilization of various water sources is necessary due to increasing population and the consequent need of agricultural development. One of the main concerns in the coming years is soil salinity and its related stress. Therefore of the important medicinal plants which is extensively cultivated throughout the world (Matricaria chamomilla L. from the Asteraceae family) was treated in a factorial experiment based on a completely randomized design with NaCl at 4 levels (0, 40, 70, 100 mM) and KCl at 2 levels (0 and 0.7 mM) and 3 replicates in order to evaluate the alleviating effects of K+ on NaCl stress. Physiological and morphological traits such as leaf area, fresh and dry weights, relative water content, etc. were measured and evaluated under stress condition. Results showed a significant effects on most measured traits at statistical levels (P≤0.05 and P≤0.01). It also revealed that Na+ is more effective. The highest and lowest values were observed in different treatments of NaCl (0-100 mM). Morphological traits were more affected by NaCl (salinity) stress, so that shoot fresh weight, shoot dry weight and root fresh weight decreased by 59, 36 and 81% respectively from control to highest Na+ level, likewise electrolyte leakage, relative water content, proline and chlorophyll content decreased from 73.11, 51.45, 0.122 and 76.28 to 62.19, 70.32, 0.094 and 20.08 respectively. Na+ and K+ contents were not significant at any stress level. Generally, it seems that using KCl on plants irrigated instead of NaCl, alleviated the harmful effects of Na+ ion and improved the growth properties of Matricaria chamomilla under stress.

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