Salinity is a major limiting factor for plant growth and development. To evaluate the impact of P5CS gene expression under in vitro salt stress condition, transgenic tobacco (Nicotiana plumbaginifolia) carrying P5CS gene and non-transgenic plants were treated with 0, 100, 150, 200 or 250 mM NaCl for 28 days. Proline content, lipid peroxidation and the activity of some antioxidant enzymes after salt treatment were measured. At 150 mM NaCl or higher, plant’s leaf and root showed an increase in proline content significantly. Malondialdehyde (MDA) level in non-transgenic plants was considerably higher than the transgenic tobacco plant at 100 mM NaCl and higher. Activities of ascorbateperoxidase (APX) and catalase (CAT) was increased in transgenic as well as non-transgenic plants by increasing salt concentrations. However, transgenic plants showed higher level of antioxidant enzymes activity than non transgenic plants. Salinity tolerance of Nicotine plumbaginifolia transgenic P5CS gene might be closely related to the accumulation of proline, CAT and APX activity and consequently suppressed level of lipid peroxidation.