OBJECTIVES: This study was conducted to explore the effectiveness of hyperbaric oxygen (HBO) in the treatment of idiopathic sudden sensorineural hearing loss (ISSNHL) and recommend the appropriate course of treatment. METHODS: 102 patients (105 diseased ears) with ISSNHL were recruited from the Department of Neurology and Otorhinolaryngology, West China Fourth Hospital, Sichuan University, between January 2018 and September 2020. Of them, 45 patients (group A) received intravenous steroid (IVS), and the remaining patients (group B) received IVS and HBO therapy (HBOT). Pure-tone audiometry (PTA) was performed twice at baseline and 10 days after treatment. Patients in group B were subdivided into group 1 (≤10 sessions) and group 2 (>11 sessions) to verify the correlation between the efficacy and course of HBOT, at the follow-up endpoint, the PTA was performed again. The multivariate logistical regression model was used to analyze the related factors of prognosis. RESULTS: Compared with the control group, significantly larger hearing gains and better hearing recovery rate were observed in the IVS + HBOT group (p < 0.05). The time of treatment and course of HBOT were significantly correlated with the hearing threshold after treatment (p < 0.05) and had no significant relationship with tinnitus and age (p > 0.05). CONCLUSION: HBOT + IVS is an effective method for ISSNHL, especially for the recovery of low-frequency hearing and initial hearing levels of severe and profound. Tinnitus is the most common concomitant symptom of ISSNHL, and prolonging the course of HBOT did not significantly improve it. Initiating HBOT within 7 days for 10-25 sessions of treatment was more beneficial.