Breast cancer is a genetic disease caused by the accumulation of mutations in neoplastic cells and is responsible for the highest morbidity. The aim of this study is to determine the amino acids in the blood serum samples of breast cancer patience. In this study, blood serum samples from 45 breast cancer patient and 32 healty individual were used. The amounts of amino acids were determined by HPLC. It was observed that, while the level of valine, tryptophan, glycine, histidine, thronine, proline, cysteine and asparagine were increased on the other hand leucine, isolatinine, phenylalanine, methionine, lysine, alanine tyrosine, glutamic acid, aspartic acid, arginine, glutamine and serine were decreased in the serum of cancer patients compared to the control group (p<0.001). When amino acid levels of the untreated and treated breast cancer groups were compared, it was observed that the amount of lysine and aspartic acid decreased significantly (p<0.001), while the amount of tryptophan increased (p<0.037) for the patients having cancer treatment. Changes in the amounts of other amino acids are statistically insignificant. Aspartic acid and arginine levels were significantly increased in non-breastfeeding breast cancer patients compared to breast-feeding patients (p<0.05), while the changes in other amino acid levels were statistically insignificant (p>0.05). Detailed studies are required to use the amino acids as biomarker for diagnising the breast cancer.