Background: Breast cancer is the most frequent cancer and the second leading cause of cancer deaths among women worldwide and an increasing incidence rate has been observed in Sudan. Objective: this study was aimed to determine the effect of breast cancer on testosterone and sex hormone binding globulin inSudanese female patients. Materials: This study included 120 untreated breast cancer patients with clinical and histopathological evidence and 100 healthy volunteers as a control. Venous blood was drawn from the cases and controls. Methods: Testosterone and sex hormone binding globulin were estimated in blood samples by using radio-immune assay. Paired t-test was used to compare the mean serum levels of testosterone and sex hormone binding globulin between patients and controls. Results: In the present study there were significant high levels of serum testosterone in premenopausal lady patients with breast cancer as compared to control group (p value __ampersandsignlt;0.05). On the other hand, there were significant low levels of sex hormone binding globulin in ladies with breast cancer when compared to controls (p value__ampersandsignlt;0.05). Conclusion: A significant high level of testosterone and low level of sex hormone binding globulin were found in this study.