Serum autoantibodies against p53 (p53Ab) have been identified in patients with various tumors and are used as one of molecular markers. Here we examined the possible application of p53Ab for diagnosis of breast cancer. We collected sera from 141 patients with breast cancer and determined the p53Ab level by enzyme-linked immunosorbent assay with MESACUP anti -p53 test ELISA kit. The positive rate of p53Ab was greater than those of current molecular markers, breast cancer antigen -225 (BCA225), carcinoembryonic antigen (CEA), and carbohydrate antigen 15-3 (CA15-3). We found no significant relationships between the p53Ab level and patient's clinical characteristics including age, tumor size, and metastasis. Further, the value of p53Ab did not correlate with other serological tumor markers and expression levels of hormonal receptors (estrogen receptor and progesterone receptor) and HER2. The sensitivities of BCA225 and CEA were relatively low in early stages and increased in a stage-dependent manner while the positive rate of p53Ab was sustained from early to late stages at a high level (14.6% and 15.4%, respectively). Combinations of p53Ab with BCA225, CEA, and CA15-3 improved the positive rate to 20.6%, 21.2%, and 26.7%, respectively, which were greater than the positive rate obtained by combinations of other serological markers. Thus, serum p53Ab is a useful molecular marker of breast carcinoma and we recommend the combination assay with other serological markers for clinical diagnosis.