In order to investigate the effects of mycorrhiza, phosphor, and salt stress on phosphor concentration in shoot and morphological traits of alfalfa (Medicago scutellata L.) a pot experiment was conducted in a factorial based on a randomized complete design with four replications at Agricultural Research Station in Gonbad Kavous University, Iran during growing season in 2012-2013. The treatments were the combination of mycorrhiza factors (lack of mycorrhiza inoculation and mycorrhiza inoculation), phosohor fertilizer factor (0, 50 and 100 mg kg^-1 soil) and water salinity factors (irrigation by water salinity zero, 2 and 4 ds m^-1). Results showed that mycorrhiza inoculation had a significant effect on the increase of root dry weight and shoot dry weight, root to shoot dry weight ratio, root length, colonized root length, the percentage of root colonization and phosphor concentration in shoot. However with the application of phosphor, shoot dry matter, root to shoot dry matter ratio and root length and phosphor content of shoots were increased significantly. Water Salinity significantly reduced root length. The highest amount of root dry weight, shoot dry weight, root to shoot dry weight ratio and phosphor concentration in shoot were obtained from mycorrhiza inoculation and 100 mg kg^-1 soil phosphorus. The results showed that application of phosphorus fertilizer and mycorrhiza through symbiosis with plant and via developing its mycelium in soil, caused better water and nutrient element absorption, thereby improving the growth and development of the plant.