Various processed foods and beverages have been manufactured using deep seawater (DSW), desalted DSW (dDSW), and concentrated DSW in Japan. To confirm the safety of dDSW, we investigated hematologic and blood chemical effects of dDSW in mice. The dDSW and desalted surface seawater (dSSW) were diluted to 6.7%, 10%, and 20% with purified water. BALB/c mice were housed for 12 weeks, and administered the diluted dDSW, dSSW, or purified water as a control during the period. The results for dDSW were compared with those for dSSW and purified water. None of the groups of mice showed any clear abnormal growth or behavior; neither did any show signs of illness nor a single case of death during the 12 weeks study. We found no significant differences between the dDSW and control groups in terms of red blood cell count, hemoglobin, hematocrit, white blood cell count, and neutrophil counts, whereas white blood cell and lymphocyte counts were significantly higher in the 10% dSSW group at the end of 4 and 12 weeks than those in the control group. A significantly higher triglyceride level was detected only in the 6.7% dSSW group. Our results show no evidence of acute or subacute effects of diluted dDSW. Effects of diluted dDSW on hematologic and blood chemical values in mice are thought to be similar to those of purified water. This finding suggests that dDSW is as safe as purified water for drinking water.