Mammography, magnetic resonance imaging (MRI), and ultrasound are useful tools that can be used in breast cancer (BC) screening but these methods have various limitations. Thus, finding diagnostic biomarkers may be a useful alternative choice. A total of 142 females with breast diseases (40 females with benign conditions and 102 females with BC) were included in the study. In addition to age-and sex-matched 29 normal females as a negative control. The level of collagen III was detected using the ELISA technique. It was (21.29±3.14 µg/ml) in sera of females with BC higher than in benign (13.91±2.65 µg/ml) and in normal (5.69±0.43 µg/ml) females. Collagen III yielded an AUC of 0.86 to differentiate BC from normal females and an AUC of 0.62 to differentiate BC females from those with benign conditions. Moreover, AUC was risen to 0.72 to differentiate females with BC from those without BC. While the index provided values that were significantly (P<0.01) higher in BC (9.1±1.3) than benign (6.3±1.1) and normal (2.5±1.1) females. It yielded an AUC of 0.98 (sensitivity = 90.0 %) to differentiate BC from normal females and an AUC of 0.84 to differentiate BC females from those with benign conditions. Moreover, AUC was risen to 0.87 to differentiate females with BC from those without BC (sensitivity = 84.0 %). In conclusion, serum collagen III concentration represents a candidate biomarker for BC. Moreover, its combination with cancer antigen 15-3 (CA 15.3) and age provided a valuable index for BC diagnosis with high accuracy.