Objective To investigate the knowledge, attitudes, and behavioral cognition regarding hydrogen-oxygen therapy in mitigating the side effects of anticancer drugs among malignant tumor patients, so as to provide theoretical support for optimizing treatment regimens, enhancing therapeutic efficacy, and improving patient quality of life. Methods A total of 120 malignant tumor patients undergoing anticancer drug therapy and hydrogen-oxygen inhalation therapy at The First Affiliated Hospital of Naval Medical University from 2022 to 2023 were enrolled by simple random sampling method. A self-designed questionnaire was used to assess the patients’ knowledge of hydrogen-oxygen therapy, their attitudes toward it, and their perceptions about the behavior when using it. Results A total of 120 questionnaires were distributed, with 114 returned, yielding a valid response rate of 95.0%. Patients demonstrated relatively good knowledge of hydrogen’s characteristics and functions, though perceptions of its safety still had room for improvement. Overall, patients held positive attitudes toward hydrogen-oxygen therapy. However, their perception regarding the correct use of hydrogen-oxygen therapy exhibited deviations. The perception regarding the correct use of hydrogen-oxygen therapy was influenced by gender, age, marital status, educational attainment, average monthly household income, living arrangements, and presence of chronic comorbidities (all P＜0.05). Conclusion Cancer patients have some awareness that hydrogen-oxygen therapy can alleviate the side effects of anticancer drugs and generally hold positive attitudes toward it. Nevertheless, targeted education is still needed to disseminate knowledge about its therapeutic efficacy and to promote its proper use, so as to improve the patients’ comprehensive understanding and acceptance of hydrogen-oxygen therapy.