This study was conducted to evaluate the effect of zinc application at different levels (10, 20 and 40 mg/kg soil) as ZnSo₄ .7 H₂O on growth and chemical composition of Swietenia macrophylla under salinity stress at three concentrations (2000, 4000 and 6000 ppm) NaCl. Tap water was used as control. The results revealed that, salinity at 6000 ppm caused death of seedlings. Salinity levels (2000 and 4000 ppmNaCl alone) significantly decreased survival percentage and growth parameters (stem length, stem diameter, leaf area, leaves number, root length and fresh and dry weight for plant parts. Also, salinity decreased N,P,K, Ca, Mg, Zn, Chlorophyll and total carbohydrates in plant parts. While, salinity increased Na, Cl and proline content when compared to control. Zn application increased survival percentage and growth parameters (stem length, stem diameter, leaf area, leaves number, root length and fresh and dry weight for plant parts under salinity stress when compared to salinity treatments without Zn. Also, Zn application increased  NPK, Ca, Mg, Zn, Chlorophyll and total carbohydrates in plant parts. While, Zn decreased Na, Cl and proline content. In this study 20 mg Zn /kg soil recorded the best result with three salt concentrations.