Objective:To determine the prevalence of cognitive disorders in patients suffering from breast cancer receiving chemotherapy treatment in Mayo Hospital Oncology ward. Subjects and methods: A cross-sectional type of study was conducted in Mayo Hospital Lahore from April 2017 to June 2017 in order to know about the effects of chemotherapy on cognitive dysfunction in female breast cancer patients.The study included 55 participants , all of them were receiving chemotherapy at the time the research was conducted. A questionnaire was formulated and got filled. The final data was analyzed with the help of SPSS having version 21 and the descriptive statistics e.g percentage and frequencies were achieved. Results:Different measures to test the cognitive functions of patients were used.The analysis of data demonstrated significant relation between increasing age and deterioration of words registration functions,verbal functions and clock drawing interpretation functions of brain. (p = .001 , p=.015 , p=.006 respectively) .While financial management skills of the patients seemed to be unaffected by chemotherapy ( p =.066).Conclusion :These results of this study clearly showed serious derangement in cognitive functions of the patients receiving chemotherapy for breast cancer.Moreover age and pre-treatment natural cognitive reserve are the important predictors of magnitude of deterioration.