A549-tumor transferred SCID mice were either non-exposed or exposed to HBO2(98% O2, 2% CO2 at 2.5 ATAfor2.5 ATA 90 min 5 times in a week beginning at the 45th date after tumor injection and were monitored for the tumor volume twice in a week. Tumor volume was calculated as length (L) × width (W) × height (H). (A) The growth curve of A549 cells in SCID mice. Only the mice with tumor volume larger than 500mm3 were selected (B) The comparison of tumor volume among groups of mice before or after HBOT. For each dot-point represents the tumor volume of one A549-tumor transferred SCID mice. HBOT effectively suppressed tumor growth after 14 days (**P < 0.01) and 28 days (**P < 0.01) of tumor transfer. (C-0 represents for control mice at the first date comparing with HBOT mice; O-0 represents for mice receiving the first date of HBOT; C-14 days represents for control mice after 14 days comparing with HBOT mice; O-14 days represents for mice after 14 days of HBOT; C-28 days represents for control mice after 28 days comparing with HBOT mice; O-28 days represents for mice after 28 days of HBOT).