To evaluate the effect of salinity on mycorrhizal grass pea plants in two water supply conditions, a factorial experiment was conducted based on complete block design at Research Farm of Urmia University in 2012. Treatments were two levels of irrigation [irrigation at field capacity (FC) and 50% FC], which were applied from two-leaf stage, five levels of salinity (0, 5, 10, 15 and 20 dS/m of irrigation water from Lake Urmia) and mycorrhizal specie (inoculated by Glomus mosseae and non-inoculated treatment as control). Results of ANOVA showed the significant interaction among mycorrhizal, salinity and irrigation on the protein per cent and protein yield. Interaction between water deficit stress and salinity stress significantly decreased chlorophyll, protein per cent and protein yield, whereas the application of mycorrhizal fungi compensated the stress damages. The highest protein per cent (17.75) and protein yield (0.82 g/plant) were obtained from mycorrhizal plants irrigated at 100% of field capacity by non-saline water (0 dS/m). The highest chlorophyll a (4.6 mg/g) and carotenoid (1.42 mg/g) were obtained from mycorrhizal plants affected by non-saline water (0 dS/m). These findings strongly suggested that the irrigation intervals of Lathyrus sativus could be increased by application of mycorrhizal fungi without significant reduction in productivity.