Hydrogen peroxide poisoning is a rare but potentially severe poisoning that can cause digestive tract irritation and/or gas embolism when ingested. The clinical presentation varies from asymptomatic patients to severe embolic consequences or even death. There is little evidence on the treatment of such poisoning to guide physicians in caring for these patients. This paper reports on two cases of highly concentrated hydrogen peroxide poisoning after accidental ingestion. Both patients showed evidence of portal venous gas, with one patient exhibiting significant symptoms while the other did not. Both were treated with hyperbaric oxygen therapy (HBOT), with a follow-up CT scan revealing a complete resolution of the portal venous gas. This suggests that HBOT is effective for both symptomatic and asymptomatic patients with portal venous gas and should be considered as an effective treatment option in cases of highly concentrated hydrogen peroxide poisoning.