Background and Objective: Breast cancer is the most common cancer and the second leading cause of cancer death among women worldwide. Mammography is a sensitive and specific test that is used for early diagnosis of breast cancer. Mammography screening behavior is one of the behaviors that early study on its stage of change can be used in proper planning and effective interventions for performing mammography screening behavior. This study was done with the aim of determining mammography screening behavior stage of change among women aged 40 and older in Isfahan. Materials and Methods: In this descriptive population-based study, 384 women aged 40 and older were recruited by random sampling method in the city of Isfahan. Mammography screening behavior stage of change was determined by the Rakoweski stage of change questionnaire. The data were analyzed by SPSS software using statistical chi-square and ANOVA at the significant level of α = 0.05. Results: The mean age of the women was 52.24 ± 8.22 years. The results indicate that 36.2%, 21.1%, 4.2%, 6.2%, and 32.3% of the women studied were in the stages of Pre-contemplation, Contemplation, Action, Maintenance, and Relapse, respectively. The statistical analysis show that there were some significant correlationship between age (p<0.0001), education (p= 0.009), married status (p= 0.011), insurance status (p= 0.025) and income level (p= 0.009) with the stages of change. Conclusion: Our results demonstrate that the majority of subjects were in the pre-contemplation and contemplation stages, and that a low percentage of women were in the action and maintenance stages. Therefore, appropriate intervention based on stage of change for promotion of mammography screening behavior seems to be essential.