Objective To develop the Lymphedema Preventive Behavior Intention Scale for Postoperative Breast Cancer Patients (LPBISPBCP), and test its reliability and validity, so as to provide a reliable assessment tool. Methods Based on the Health Action Process Approach, the initial scale was formed through literature review, semi-structured interviews and expert consultation.A total of 672 postoperative breast cancer patients were recruited by convenience sampling from February to July 2025 for psychometric testing. Results The scale consisted of 6 dimensions including self-efficacy, positive outcome expectation, negative outcome expectation, risk perception, behavioral intention and implementation intention, with 39 items in total.The cumulative variance contribution rate was 78.155%.The item-level content validity index ranged from 0.867 to 1.000, and the scale-level content validity index was 0.958.The Cronbach′s α coefficient, Spearman-Brown split-half reliability and test-retest reliability were 0.932, 0.706 and 0.785 respectively.Confirmatory factor analysis showed χ2/df=1.649，RMSEA=0.041，CFI=0.949，IFI=0.949，TLI=0.944, indicating good model fit of the scale. Conclusion The scale has good reliability and validity, which can be used as an effective tool to evaluate lymphedema preventive behavior intention in postoperative breast cancer patients.