Two experiments were conducted in the laboratory at the College of Agricultural and Marine Sciences and in the shadehouse at the Agricultural Experimental Station in Sultan Qaboos University to examine the physiological basis of salt tolerance of three local desert trees (Simr (Acacia tortilis), Ghaf (Prosopis cineraria) and Sidr (Ziziphus spina-christi)]. The laboratory study investigated the effect of different salinity concentrations on seed germination rate and percentage of target species. The shadehouse study investigated the effect of different salinity concentrations on the chlorophyll content, nitrogen concentrations and proline accumulation of tree species. In the laboratory study, the experiment was a complete randomized design (CRD) with 35 seeds per variety. There were 6 treatments, consisting of five salinity treatments plus control for each of the three tree species with four replications. Six observations were made during 18- day period to evaluate seed germination. Salt tolerance was compared on the basis of both final seed germination and rate of germination. A. tortilis and Z. spina-christi had superior germination performance at low and moderate levels of salt stress. A. tortilis was identified as more tolerant, being able to germinate rapidly under both control (no stress) and salt stress conditions. Z. spina-christi germinated rapidly under control conditions but germinated poorly at the highest salt stress levels, thus exhibiting higher sensitivity to salt. In the shadehouse study, three concentrations of salinity, viz. low (tap water as control), medium (6 dS m*'), and high (12 dS m') were utilized. Plants were one-year old at the start of the treatments. The results of salinity application to each tree was examined once every month over a period of 90 days. The experiment was laid in completely randomized design (CRD) using 20 seedlings for each salinity application. The effect of different salinity concentrations on total chlorophyll content, proline accumulation and nitrogen concentrations was studied. A, tortilis accumulated more total chlorophyll than the other two species at the different s alinity treatments. A. tortilis seedlings were least sensitive to medium levels of salinity throughout the first three months of growth and were affected most by high levels of salinity during the first two months, showing significant recovery by the third month. A. tortilis accumulated less proline at moderate levels of salinity than did other two species, a finding which recommends this species for use in low to moderate saline conditions.