Objective To explore the effect of internet⁃delivered cognitive behavioral therapy (ICBT) on post⁃traumatic growth in breast cancer patients undergoing chemotherapy. Methods A total of 84 breast cancer patients undergoing chemotherapy were selected as the research subjects, and they were assigned to control group or observation group, with 42 cases in each group. The control group received routine nursing for intervention, based on which the observation group received ICBT intervention. The scores of Post⁃Traumatic Growth Inventory (PTGI), Self⁃Rating Anxiety Scale (SAS), Self⁃Rating Depression Scale (SDS), and Functional Assessment of Cancer Therapy⁃Breast (FACT⁃B) scale score before intervention and 4 weeks after intervention were compared between the two groups. Results After 4 weeks of intervention, the observation group exhibited higher scores of PTGI, various dimensions of FACT⁃B scale, and a higher total score of FACT⁃B scale, whereas lower scores of SAS and SDS as compared with before intervention and the control group (P<0.05). Conclusion ICBT can relieve anxiety, depression, elevate post⁃traumatic growth level, and ameliorate quality of life in breast cancer patients undergoing chemotherapy.