Background: This study examined perceived cognitive function in patients with breast cancer and determined the main predictors of changes in cognitive function following treatment.Methods: The analytical cross-sectional study was performed in this study. 96 women receiving adjuvant treatment after surgery and who had already received adjuvant treatment were included in the study. The convenience sample was selected from the list of patients in Cancer Registry Center, private clinics and the Oncology Ward of Imam Khomeini Hospital in Ardabil, Iran. We used the Attentional Function Index to measure perceived cognitive function. SPSS version 16.0 was used to analyze the data. We used the t-test and analysis of variance to compare the differences in the Attentional Function Index scores to demographic and medical characteristics.Results: The mean Attentional Function Index score was 59.53±1.69. There was a statistically significant difference between the scores in terms of current non-surgical treatment (P<0.000). Regarding the time elapsed after disease diagnosis, the difference between the Attentional Function Index scores was statistically significant (P<0.00).Conclusion: Chemotherapy and hormone therapy can act as risk factors for cognitive impairment in patients with breast cancer.