Objective To explore the influence of self-disclosure intervention based on positive psychology theory on mood of breast cancer patients undergoing chemotherapy following breast cancer surgery. Methods Breast cancer patients undergoing chemotherapy following breast cancer surgery were divided into a control group (n=45) and an intervention group (n=43) according to the units they were admitted to. The control group received routine chemotherapy care, while the intervention group was additionally subjected to self-disclosure intervention based on positive psychology. The levels of self-disclosure, negative emotions and fear of cancer recurrence were compared between the two groups before and after intervention. Results After the intervention, self-disclosure scores in the intervention group were significantly higher than those of the control group; scores of inward and outward irritability, depression, anxiety, and cancer recurrence fear in the intervention group were significantly lower than those of the control group (P<0.05 for all). Conclusion Self-disclosure intervention based on positive psychology theory for patients undergoing chemotherapy following breast cancer surgery, can effectively improve self-disclosure level of patients, alleviate negative emotions, and reduce their fear of cancer recurrence.