The present study aimed to assess the effects of salinity stress on some physiological and morphological characteristics and plant yield of Marsh Mallow ( Althaea officinalis ). Nitrogen fertilizer application has been used as a way to reduce damages caused by salt stress. This experiment was carried out in a completely randomized design in a factorial experiment on Chaah Anari field of Isfahan University of Technology located in Khomeinishahr of Isfahan province. Salinity stress was applied at four levels of 0, 2, 6 and 10 dS/m and nitrogen at four levels of 0, 50, 100 and 150 kg.ha -1 . Mild salinity at 2 dS/m resulted in an increase in chlorophyll a, chlorophyll a/b ratio, carotenoid, anthocyanin, leaf relative moisture content, altitude and dry weight of the shoot, while severe salinity at 10 dS/m, caused reduction on all of these traits, also the content of chlorophyll b, total chlorophyll, potassium, calcium, leaf area and number of leaves, shoot dry weight and mucilage of the Marsh Mallow leaves. Proline content increased At 6 dS/m, and sodium concentration, Na + /K + and Na + /Ca 2+ ratios increased at 10 dS/m salinity level. Increasing the concentration of nitrogen fertilizer to 150 kg.ha -1 increased the photosynthetic pigments (chlorophyll a, chlorophyll b, chlorophyll a/b ratio, total chlorophyll, carotenoid and anthocyanin), proline, potassium and calcium concentration, leaf area and number, shoot dry weight and leaf mucilage and decreased sodium concentration, Na + /K + and Na + /Ca 2 + ratio of leaves. The level 100 kg .ha -1 nitrogen fertilizer increased leaf relative moisture content, height and shoot dry matter. The amount of photosynthetic pigments increased with nitrogen application under salt stress conditions. The highest content of chlorophyll a and chlorophyll a/b ratio was related to 2 dS/m salinity and 150 kg N.ha -1 with 193 and 211% increase compared to control treatment. The highest content of chlorophyll b was related to non-stress treatment and consumption of 150 kg N.ha -1 , which increased 21% compared to control treatment. The highest total chlorophyll content was related to control treatment and 2 dS/m of salinity treatment both under 150 kg N.ha -1 , which was 18.20 and 17.63 mg/g leaf fresh weight respectively. The lowest content of photosynthetic pigments were under 10 dS/m and no nitrogen fertilizer application. Under the interaction of salinity and nitrogen levels, the highest sodium concentration and Na + /K + and Na + /Ca 2+ ratios were related to 10 dS/m salinity and no nitrogen application, which was respectively 342, 546 and 763% higher than the control treatment, while the highest amount of calcium was related to non-stress treatment and 150 kg N.ha -1 . The interaction between salinity and nitrogen levels showed that the highest height was related to salinity treatment 2 dS/m and consumption of 100 kg N.ha -1 , which increased 65% compared to the control. The highest area and number of leaves per plant were related to non-stress treatment and 150 kg.ha -1 nitrogen which was 56% and 60% higher than the control treatment, respectively. The highest shoot dry weight was related to non-stress treatment and 50 kg.ha -1 nitrogen, which did not show statistically significant differences with 100 and 150 kg N.ha -1 . The highest leaf mucilage was related to non-stress treatment and consumption of 150 kg N.ha -1 , which increased 171% more than control treatment. From the results of this study, it can be concluded that shoot dry weight and leaf mucilage weight decreased significantly under salinity increasing. At least partly was due to the reduction of chlorophyll content and toxic effects of chlorine and sodium ions because such changes impair the photosynthetic activity of the plant, resulting in a decrease in dry weight and leaf mucilage; However, the use of nitrogen fertilizer up to 100 kg.ha -1 can reduce the negative effects of salinity stress partly by effecting on physiological activities, while consumption more reduces the shoot dry weight of the plant. Keywords: Marsh Mallow, Salinity, Nitrogen, Proline, Mucilage, Shoot yield