Abstract: Basil (Ocimum basilicum) seedlings were subjected to 0, 5%, 10%, 20%, 30% and 40% seawater under netting house conditions. Increasing seawater concentration led to considerable reduction in plant growth rate and dry mass accumulation. However, root growth was not affected even by treatment with 30% seawater. High salinity (30% and 40% seawater) caused significant increases of soluble sugar and proline contents as well as leaf water use efficiency, whereas photosynthesis was inhibited mainly due to stomatal restriction. Accumulation of Na⁺ was correlated with a decline of Ca²⁺ and K⁺ in stems, roots or both. However, contents of K⁺ and Ca²⁺ in leaves increased or remained relatively unchanged with increasing salt levels. In plants stressed by salinity, Na⁺ were partitioned mainly in roots (57.1%-64.6% of the total) and more than 50% of the K⁺ and Ca²⁺ were stored in leaves. In addition, seawater stress decreased the K⁺/Na⁺ and Ca²⁺/Na⁺ in this species, although the higher K⁺/Na⁺ and Ca²⁺/Na⁺ were observed in leaves rather than in roots and stems. The K⁺/Na⁺ was greater than three even when subjected to 40% seawater. These results suggest that salt tolerance of basil plants might be associated with the compartmentalisation of Na⁺ in roots and the balance of K⁺, Na⁺ and Ca²⁺ in leaves as well as the osmotic adjustment with soluble sugar and proline under conditions of high salinity.