Iran contained diverse and valuable medicinal and ornamental plants. About 15 percent of cultiveted of Iran subjected to salinity and ongoing studies report an increasing trend of salinization. Myrtus communis L. is a diploid plant belonged to family of Myrtaceae as an important medicinal and ornamental plant. One of the most important breeding objectives in medicinal plants, is increasing of the level of antioxidant compounds in these plants however, such compounds may be affected by environmental conditions. So, the present study was aimed to investigate the effect of salinity stress on morphological, physiological, phytochemical and antioxidant activity in Myrtus communis L. This study was conducted in an experiment of lit plot in time according to a randomized complete block design with four replicates and four salinity including control and 2, 4 and 6 dS and three harvest times (early spring, early summer and early fall). According to the evelution of morphological characteristics, during all three periods, vegetative growth except secondary branches and flowering time was reduced under salinity stress. Chlorophyll, SPAD and leaf relative water content (RWC) were found to be decreased and proline and carotenoids (at the time of spring and summer) increased under salinity stress treatments. As results showed, the highest level of secondary metabolites were recorded in spring and summer harvest times. In the autumn, the phenolic compounds, antioxidant activity, flavonoids, essential oil were low compared to others seasons. Moderate salinity stress to 4 dS and spring/ summer harvest time increased essential oil content and salinity stress up to 6 dS and spring/ summer harvest time elevated phenolic compounds (96.96) and flavonoids (8.24) and the antioxidant activity compared to autumn. A comparative study between the three methods of antioxidant activity measurments in three harvest times showed positive correlation between the three methods including DPPH, FTC and beta-carotene in the first and second harvest times. At third harvest time, DPPH and FTC were positively correlated, while beta-carotene was not in line with two above methods. As salinity stress in spring and summer, antioxidant activity was intensified which is probably attributed to the high level of plant phenolic compounds in the spring and summer. The results of GC (Gas Chromatography) analysis showed that ?-pinene and 1.8 cineole was increased under salt stress compared to control.Finally, In order to achieve the highest yield, spring and summer harvest time and 4 dS stress condition were introduced as the best conditions for myrtle growth. Key words : antioxidant activity, harvest time, Myrtle, salinity stress