Soil salinity and phosphorus (P) deficiency both have adverse effects on crop growth and productivity, but the interaction of soil salinity and P deficiency is not well known. Two P-inefficient wheat cultivars, Janz (salinity-tolerant) and Jandaroi (salinity-sensitive), grown in soil in rhizoboxes, were treated with either 100 µM P (control), 100 mM NaCl (saline stress), 10 µM P (low P stress), or both NaCl and low P (combined stress), from 10 days after sowing (DAS) until harvest at 40 DAS. Significant reductions in leaf area, shoot and root biomass, tissue water and chlorophyll contents, gas exchange, and K+ and P acquisition at harvest were observed in the three treatments. The reduction was greater for low P supply than for salinity alone, but their interaction was not additive. The detrimental effects on root growth became apparent 10 days earlier in Jandaroi compared to Janz. Root length, root number, root length densities, and root number densities were higher in the upper 10 cm soil layer than in the lower layers for both cultivars. This study demonstrated that 10 µM P is more detrimental than 100 mM NaCl for shoot and root growth of both wheat cultivars irrespective of their difference in salinity tolerance.