Purpose <p>This study aims to evaluate the effects of hyperbaric oxygen treatment (HBOT) on new bone formation after sinus lift operation in diabetic rabbits.</p> Methods <p>27 New Zealand White rabbits that were alloxan monohydrate-induced diabetics were divided into four groups following the sinus lift procedure. Hyperbaric oxygen treatment was applied to 14 rabbits in experimental groups (HBOT-1, HBOT-2). Subjects were sacrificed after 4 (HBOT-1, C-1) and 8 (HBOT-2, C-2) weeks. Histomorphometry and immunohistochemistry were used in histopathological evaluation.</p> Results <p>The new bone area in the HBOT-1 group is statistically more significant than the C-1 group (<i>p</i> = 0.002) and the new bone area in the HBOT-2 group is statistically more significant than the C-2 group (<i>p</i> = 0.001). The area intensity and severity of staining with anti-collagen I in HBOT-1 group is statistically significant compared to C-1 group (<i>p</i> = 0.001) and in HBOT-2 group compared to C-2 group (<i>p</i> = 0.001). The area intensity and intensity of staining with anti-BMP-2 in the HBOT-1 group is statistically significant compared to the C-1 group (<i>p</i> = 0.000) and in the HBOT-2 group compared to the C-2 group (<i>p</i> = 0.001). The number of new vessels in HBOT-2 group is statistically significant compared to C-2 group (<i>p</i> = 0.000).</p> Conclusions <p>Hyperbaric oxygen treatment in the long and short term increases new bone formation, and intensity the level of collagen type I, bone morphogenetic protein-2, and the vascular endothelial growth factor level, in the long term. Based on these results, it was concluded that the negative impact of diabetes on new bone formation can be recovered with hyperbaric oxygen treatment.</p>