Salinity depresses ion activities, decreases the ratios of plant nutrients to Na and Cl ions, and consecutively suppresses plant growth. The objective of the present study was to distinguish the effects of NaCl and $Na_2 SO_4$ salinity on the growth, ionic relations and proline accumulation of tomato plants. Tomato plants were grown for two months. Plant growth was reduced, but proline accumulation was enhanced by salinity. Total N and $NO_3$-N content of plants were decreased by both NaCl and $Na_2 SO_4$ salinity. Sulphur content was not affected by the salt treatments. Salinity caused nutrient imbalances. The Na and Cl contents of plants increased while the K:Na ratio and $NO_3$-N:Cl ratio decreased. In addition, the nutrient uptake rate was depressed by salt treatments. All parameters measured were affected more adversely by $Na_2 SO_4$ than by NaCl salinity. The depressing effect of $Na_2 SO_4$ applied during the first month of the growing period was more deleterious than $Na_2 SO_4$ applied during the second month of the growing period.