Objective To analyze the potential categories and influencing factors of physical activity （PA） change trajectories of breast cancer patients during chemotherapy, so as to provide reference for the follow-up physical activity intervention for patients with PA different characteristics.Methods From February 2024 to May 2024, 211 patients on chemotherapy were selected by using conve-nience sampling method.The baseline data of patients were collected using the general data questionnaire, the Strategies Used by People to Promote Health scale, the MD Anderson Symptom Inventory, and the Family APGAR Index.The long form of the International Physical Activity Questionnaire was used to evaluate their PA levels at four time points:before chemotherapy, before the second course, before the fouth course, and before the sixth course of chemotherapy.The latent growth mixture model was applied to identify the trajectory classes, and multivariate logistic regression was used to analyze the influencing factors of the PA change trajectory in breast cancer patients on chemotherapy.Results The change trajectory of PA in breast cancer patients on chemotherapy could be classified into "moderate PA level decreased-midterm recovery group" （19.4%）, "moderate PA level decreased-late recovery group" （54.5%）, and "low PA level maintenance group" （26.1%）.The results of multivariate logistic regression analysis showed that age, symptom distress, symptom severity, family care, and self-management efficacy were the influencing factors of the PA trajectory classes in breast cancer patients on chemotherapy （all P＜0.05）.Conclusion PA of breast cancer patients on chemotherapy shows group-based heterogeneity.Medical staff should formulate targeted intervention measures based on the characteristic of groups and influencing factors of the PA change trajectory of patients to improve their PA levels.