Abstract A few years of stigmasterol research brought into light several vital functions of this new group of phytohormone in plant growth and development. New discoveries of the physiological properties of stigmasterol allow us to consider it as a highly promising, environmentally-friendly natural substance suitable for a wide application in plant protection and yield promotion in agriculture. In the present work we studied the effect of flax seed soaking in stigmaterol (200 ppm) on growth, hormonal contents, total phenol, phenylalanin ammonia lyase (PAL) activity, in addition to fiber composition, yield components and the quality of the yielded seeds and fibers of Linum usitatissimum L.cv. Sakha 2 plants grown under different salinity levels. We proved that stigmasterol is phytohormone with a pleiotropic effect. It has a promotive effect on growth, hormonal contents, PAL activity, fiber quality, seed oil content and all the yield characteristics under normal conditions of growth. Moreover, stigmasterol improves the nutritional value and the economic importance of the flax seed oil by increasing linolenic acid and oleic acid contents. It also helped to overcome stress provoked by NaCl as we reported that seed soaking in stigmasterol gives plants some halophytic characteristics which enable the plant to partially alleviate the drastic effect of all the used concentrations of NaCl.