Application of deep sea water (DSW) on preparation of green tea was evaluated. Green tea leaves were soaked in desalinated deep sea water (DSW) at 75°C for 10 min, and were evaluated for antioxidant activity and catechin content. DSW green tea showed higher antioxidant activity than green tea prepared with distilled water (DW). The 2,2-diphenyl-1-picrylhydrazyl (DPPH) radical scavenging activities and reducing power of DW and DSW green teas were 57.88 and 83.98%, and their optical densities were 0.99 and 1.14, respectively. Nitrite scavenging activity was also higher in DSW green tea than in DW green tea. Overall amounts of catechins and caffeine were also greater in DSW green tea. For example, epigallocatechin gallate content in DW and DSW green teas were 13.20 and 17.97 mg/g, respectively. However, there was no significant colour difference between the two tea preparations. These results indicated that the chemical properties of green tea are significantly affected by DSW and that DSW results in high quality green tea. Key words: Green tea, deep sea water, antioxidant activity, catechins.