The present study was aimed to evaluate the effect of irrigation water salinity on some agronomic and physiological attributes of purslane (Portulaca oleracea L.) and its tolerance to salinity stress. The treatments included seven levels of electrical conductivity of irrigation water (0.6 (control), 3, 6, 9, 12, 15, and 18 dSm−1) arranged in the form of a completely randomized design with three replications. The results showed that salinity stress successively decreased agronomic attributes such as root, shoot, and stem dry weight, plant height and leaf area. Physiological attributes such as relative water content as well as ion leakage differently responded to salinity stress. Relative water content response to salinity followed a quadratic regression model with the maximum of 81% at electrical conductivity of 6.87 dSm−1 and the minimum of 65% at highest salinity level of 18 dSm−1. Following an exponential regression model, ion leakage remained relatively the same till irrigation water salinity of 15 dSm−1 and reached to the maximum of 78% at highest irrigation water salinity of 18 dSm−1. In addition, shoot potassium content of purslane under non saline conditions equaled to 11% that was around 10 times more than the typical of potassium sufficient concentration for adequate growth. Moreover, with increasing salinity stress, shoot potassium content decreased to 7% at highest salinity level of 18 dSm−1 of irrigation water. However, with increasing irrigation water salinity, sodium shoot content of purslane was increased from 1.9% at the lowest salinity stress to 6.7% at the highest salinity stress. Based on the linear and nonlinear models, 10% of purslane biomass reduction occurred at soil electrical conductivity of around 10 dSm−1. In addition, 25 and 50% yield reduction observed at 16 and 25 dSm−1 of electrical conductivity of soil saturated paste. Therefore, purslane can be considered as a very salt tolerant plant, halophyte, and can successfully grow in soils with electrical conductivities not suitable for most crops.