Hyperbaric Oxygen Therapy (HBOT) is increasingly applied in different areas of medical practice. The oxy-hyperbarism effects are not well understood in cancer malignancy. One unique feature of cancer is the presence of hypoxic regions that are insensitive to conventional therapies. It is possible to alter the hypoxic state and produce reactive oxygen species for better treatment outcome by HBOT. In the present study, we determined the effects of HBOT on angiogenesis, a signature of cancer progression, by using the chick chorioallantoic membrane (CAM) in vivo assy. CAMs were exposed to 2.0 ATA (atmospheres absolute) for 30 min of hyperbaric oxygen on the 6 th and 7 th days of incubation (ED6, ED7). On the 10-11 th day of incubation, CAMs were excised from eggs, fixed and analysed using APERIO ImageScope software. HBOT outcomes were evaluated quantifying the volumetric area occupied by blood vessels and calculating the number of blood vessel ramifications. Results indicated that CAMs treated at ED6 and ED7 had a significantly higher CAM vascularization and an increased number of blood vessel ramifications (+82% higher for ED6) compared to untreated CAMs (ED6=63.3±2.5 and ED7=57.7±5.5 vs. CTRL=34.7±2.5). Thus, HBOT induces an angiogenic response in treated CAMs through a classic sprouting mechanism.