Objective To explore the effect of mindfulness based stress reduction therapy on physiological stress indexes and perceived stress in patients undergoing breast-conserving surgery for young breast cancer. Methods A total of 106 patients with young breast cancer who underwent breast-conserving surgery in our hospital from August 2022 to August 2024 were selected as the research subjects. According to different nursing plans, they were divided into the control group and the study group, with 53 patients in each group. The control group received conventional nursing, and the study group received mindfulness based stress reduction therapy on the basis of the control group. The physiological stress indexes, perceived stress, psychological state and complications were compared between the two groups. Results After intervention, the levels of Cor, Ang-Ⅱ and NE in the study group were all lower than those in the control group (P <0.05). After intervention, the scores of tension, sense of loss of control, and the total score of perceived stress in the study group were all lower than those in the control group (P <0.05). After intervention, the score of positive emotion in the study group was higher than that in the control group, and the score of negative emotion in the study group was lower than that in the control group (P <0.05). The incidence of complications in the study group (5.66%) was lower than that in the control group (18.87%) (P <0.05). Conclusion Implementing mindfulness based stress reduction therapy for patients undergoing breast-conserving surgery for young breast cancer can effectively improve the physiological stress indexes, relieve their perceived stress, help to regulate the psychological state of patients, and reduce the incidence of postoperative complications.